SECTION V.. The Alimentary Tract With Its Appendages, the Spleen, and the

THE ALIMENTARY TRACT WITH ITS APPENDAGES, THE SPLEEN, AND THE PERITONEUM.

THE ALIMENTARY TRACT, ETC.

LITERATURE.

THE MOUTH.

(Except the mucous membrane of the tongue, for which see organ of taste.)

*Ducrotay de Blainville, H. M.*, Ostéographie ou description iconographique comparée du squelette et du système dentaire des cinq classes d’animaux vertébrés. Paris, 1841.

*Erdl*, Ueber den Bau der Zähne bei den Wirbelthieren, etc. München, 1841.

*Fixen, C.*, De linguae raninae structura. Dorpat, 1857.

*Heincke, F.*, Untersuchungen über die Zähne niederer Wirbelthiere. Zeitsch. f. wiss. Zool. 1873. Vol. XXIII, p. 495.

*Hertwig, O.*, Ueber das Zahnsystem der Amphibien, etc. Suppl. to Vol. XI, Arch. f. mik. Anat. 1874.

*Hoffmann, C. K.*, Bronn’s Thierbuch. Leipzig and Heidelberg, 1873–1878. Vol. VI, p. 379.

*Holl, M.*, Zur Anatomie der Mundhöhle von Rana temporaria. Wiener Acad. Sitzungsb. 1887. Vol. XCV, Pt. III, p. 47.

*Hoyer*, Ueber die Epithelzellen der Froschzunge, sowie über den Bau der Cylinder- und Flimmerepithelien und ihr Verhältniss zum Bindegewebe. Arch. f. Anat. u. Physiol. 1858, p. 163; also Deutsche Klinik, 1857.

*Langer, C.*, Ueber das Lymphgefässsystem des Frosches. Wiener Acad. Sitzungsb. 1867. Vol. LV, Pt. I, pp. 614–621.

*Leydig*, Die Anuren Batrachier der deutschen Fauna. Bonn, 1877.

*Owen, R.*, Odontography. London, 1840–1845, p. 187.

*Reichel, P.*, Beiträge zur Morphologie der Mundhöhlendrüsen der Wirbelthiere. Leipzig, 1882; also in Morph. Jahrb. 1882, Vol. VIII, pp. 1–72.

*Santi Sirena*, Untersuchungen über den Bau und die Entwicklung der Zähne bei den Amphibien und Reptilien. Verhandl. d. phys.-med. Gesellsch. in Würzburg, 1872. Vol. II, new series, p. 125.

*Schöbl, J.*, Ueber divertikelbildende Capillaren in der Rachenschleimhaut nackter Amphibien. Sitzungsb. d. k. b. Gesellsch. d. Wiss. in Prag. 1878, p. 25; also in Arch. f. mik. Anat. 1885, Vol. XXV, p. 89.

*Schultze, F. E.*, Das Drüsenepithel der schlauchförmigen Drüsen des Dünn- und Dickdarms und die Becherzellen (of the pharyngo-oral cavity). Centralbl. f. d. med. Wiss. 1866, p. 61.

*Schultze, F. E.*, Epithel- und Drüsen-Zellen. Arch. f. mik. Anat. 1867. Vol. III, p. 137.

*Smith, W. J.*, Beitrag zur differentiellen Diagnose der Rana fusca s. platyrrhinus und Rana arvalis s. oxyrrhinus auf Grund der an den Gaumenzähnen nachweisbaren Unterschiede. Pflüger’s Arch. f. d. ges. Physiol. 1883. Vol. XXXII, pp. 581–588.

*Tomes, C. S.*, On the development of the teeth of the newt, frog, slowworm, and green lizard. Phil. Trans. 1874, p. 285.

*Török*, Untersuchungen über die Entwickelung der Mundhöhle, etc. Wiener Sitzungsb. 1866. Vol. LIV, Pt. I, p. 75.

*Waller, A.*, Microscopic examination of the principal tissues of the tongue, etc. Phil. Mag. 1846, pp. 273–290.

*Waller, A.*, On the development of the mouth and tongue of the frog. Phil. Mag. 1850. Vol. I, pp. 38–43.

*Zeller, A.*, Die Abscheidung des indig.-schwefelsauren Natrons in den Drüsen (Intermaxillary gland). Virchow’s Arch. 1878. Vol. LXXIII, p. 257.

THE OESOPHAGUS AND STOMACH.

*Biedermann*, Untersuchungen über Magenepithel. Wiener Acad. Sitzungsb. 1875. Vol. LXXI, Pt. III, p. 377.

*Bischoff*, Ueber den Bau der Magenschleimhaut. Arch. f. Anat. u. Physiol. 1838, p. 503.

*Bleyer, E.*, Magenepithel und Magendrüsen der Batrachier. Dissert. Königsberg, 1874.

*Braun*, Zum Vorkommen von Flimmerepithel im Magen. Zool. Anzeiger. 1880. No. 69, p. 568.

*Brinton*, in Cyclopaedia of Anat. and Physiol., edited by R. B. Todd. 1859. Vol. I, p. 320.

*Cobelli*, Le gliandole acinose del cardia. Wiener Acad. Sitzungsb. 1866. Vol. LIII, Pt. I, p. 251.

*Ebstein, W.*, Beiträge zur Lehre vom Bau und den physiologischen Funktionen der sogenannten Magenschleimdrüsen. Arch. f. mik. Anat. 1870. Vol. VI, p. 515.

*Ecker, A.*, Ueber die Drüsen der Magenschleimhaut. Zeitsch. f. rat. Med. 1852, p. 243.

*Foster, M.*, On some points in the epithelium of the frog’s throat. Journ. of Anat. and Physiol. 1869. Vol. IV, p. 394.

*Frerichs*, On the Stomach, in Wagner’s Handwörterbuch d. Physiol. 1848. Vol. II, p. 748.

*Glinsky, A.*, Zur Kenntniss des Baues der Magenschleimhaut der Wirbelthiere. Centralbl. f. d. med. Wiss. 1883, p. 225.

*Gonjaew, K.*, Die Nerven des Nahrungsschlauches. Arch. f. mik. Anat. 1875. Vol. XI, pp. 479–496.

*Hebold, O.*, Ein Beitrag zur Lehre von der Sekretion und Regeneration der Schleimzellen. Dissert. Bonn, 1879, pp. 21–27.

*Heidenhain, R.*, Untersuchungen über den Bau der Labdrüsen. Arch. f. mik. Anat. 1870. Vol. VI, p. 368.

*Hoffmann, C. K.*, Bronn’s Klassen und Ordnungen des Thierreichs. Leipzig und Heidelberg. 1873–1878. Vol. VI, pp. 408–412.

*Just, A.*, Zur Histologie und Physiologie des Flimmerepithels. Breslauer ärztliche Zeitsch. 1885. No. 18, pp. 205–206.

*Klein, E.*, Darmkanal, in Stricker’s Gewebelehre, p. 388, etc.

*v. Kölliker, A.*, Mikroskopische Anatomie, 1854. Vol. II, p. 147.

*Langley, J. N.*, and *Sewall, H.*, On the changes in pepsin-forming glands during secretion. Journ. of Physiol. 1880. Vol. II, pp. 261, 281.

*Langley, J. N.*, On the histology and physiology of pepsin-forming glands. Phil. Trans. 1881. Vol. CLXXII, Pt. III, pp. 663–712.

*Langley, J. N.*, On the structure of secretory cells and on changes which take place in them during secretion. Internat. Monatschr. f. Anat. u. Histol. Vol. I, pp. 69–76.

*Leydig*, Lehrbuch der Histologie. 1857.

*Nussbaum, M.*, Ueber den Bau und die Thätigkeit der Drüsen. Arch. f. mik. Anat. 1882, Vol. XXI, p. 296; 1882, Vol. XXVIII, p. 296; 1877, Vol. XIII, p. 721.

*Partsch, C.*, Beiträge zur Kenntniss des Vorderdarmes einiger Amphibien und Reptilien. Arch. f. mik. Anat. 1877. Vol. XIV, p. 179.

*Regéczy, E. N.*, Ueber die Epithelzellen des Magens. Arch. f. mik. Anat. 1880. Vol. XVIII, pp. 408–411.

*Robinson, C.*, Ueber die Lymphgefässe der Abdominaleingeweide des Frosches, etc. Froriep’s Notizen, 1846. No. 807, col. 225.

*Rollett*, Bemerkungen zur Kenntniss der Labdrüsen und der Magenschleimhaut. Untersuch. in d. Institut f. Physiol. u. Histol. zu Graz. 1871.

*Schultze, F. E.*, Epithel- und Drüsenzellen. Arch. f. mik. Anat. 1867. Vol. III, p. 174; abstract in Centralbl. f. med. Wiss. 1866, No. 4.

*Schmidt, C.*, Ueber eingenthümliche aus dem Flimmerepithel hervorgehende Gebilde. Arch. mik. Anat. 1881. Vol. XX, p. 123.

*Sewall, H.*, A note on the processes concerned in the secretion of the pepsin-forming glands of the frog. Studies in the Biol. Laborat., Johns Hopkins Univers. Vol. II, pp. 131–134.

*v. Swiecicki, H.*, Untersuchungen über die Bildung und Ausscheidung des Pepsins bei den Batrachiern. Pflüger’s Arch. f. d. ges. Physiol. 1876. Vol. XIII, p. 444.

*Trinkler, N.*, Zur Kenntniss des feineren Baues der Magenschleimhaut, insbesondere der Magendrüsen. Centralbl. f. med. Wiss. 1883, pp. 161–163.

*Trinkler, N.*, Ueber den Bau der Magenschleimhaut. Arch. f. mik. Anat. 1885. Vol. XXIV, p. 74.

*Trütschel*, Ueber die Endigung der Nerven in der Schleimhaut des Magens. Centralbl. f. d. med. Wiss. 1870, p. 115.

*Valatour*, Recherches sur les glandes gastriques et sur les tuniques musculaires du tube digestif dans les poissons ossieux et les Batraciens. Annales de Sc. nat. 1861. Series IV. Vol. XVI, p. 219.

THE INTESTINE.

*Arnstein, C.*, Ueber Becherzellen, etc. Virchow’s Arch. 1867. Vol. XXXIX, p. 527.

*Arnstein, C.*, and *Gonjaew, K.*, Ueber die Nerven des Verdauungskanals. Pflüger’s Arch. f. d. ges. Physiol. 1874. Vol. VIII, pp. 614–615.

*Auerbach, L.*, Fernere vorläufige Mittheilung über den Nervenapparat des Darmes. Virchow’s Arch. 1864. Vol. XXX, p. 457.

*Auerbach, L.*, Untersuchungen über Lymph- und Blutgefässe. Virchow’s Arch. 1865. Vol. XXXIII, p. 340.

*Auerbach, L.*, Organologische Studien.

*Billroth, T.*, Ueber die Epithelzellen der Froschzunge; der Bau, Cylinder- und Flimmerepithel und ihr Verhältniss zum Bindegewebe. Arch. f. Anat. u. Physiol. 1858, p. 159.

*Billroth, T.*, Einige Beobachtungen über das ausgedehnte Vorkommen von Nervenanastomosen im Tractus intestinalis. Arch. f. Anat. u. Physiol. 1858, p. 148.

*Brettauer* und *Steinach*, Untersuchungen über das Cylinderepithelium. Wiener Akad. Sitzungsb. 1857. Vol. XXIII, p. 303. Moleschott’s Zeitsch. 1857. Vol. III, p. 157.

*Darsch, O.*, Beiträge zur Kenntniss des feineren Baues des Dünndarms. Wiener Sitzungsb. 1880. Vol. LXXXII, Pt. III, p. 168.

*Dönitz*, Ueber die Schleimhaut des Darmcanals. Arch. f. Anat. u. Physiol. 1864, p. 367.

*Dönitz*, Ueber Darmzotten. Arch. f. Anat. u. Physiol. 1866, p. 757.

*Eberth, C. J.*, Ueber den feineren Bau der Darmschleimhaut. Würzb. naturw. Zeitschr. 1864. Vol. V, p. 23.

*Eimer, T.*, Zur Fettresorption, etc. Virchow’s Arch. 1867. Vol. XXXVIII, p. 428.

*Eimer, T.*, Ueber Becherzellen. Virchow’s Arch. 1868. Vol. XLII, p. 490.

*Eimer, T.*, Zur Geschichte der Becherzellen. Dissert. 1867.

*Eimer, T.*, Die Wege des Fettes in der Darmschleimhaut bei seiner Resorption. Virchow’s Arch. 1869. Vol. XLVIII, p. 119.

*Eimer, T.*, Zur Becherfrage. Virchow’s Arch. 1867. Vol. XL, p. 282.

*Erdmann*, Die Resorptionswege in der Schleimhaut des Dünndarms. Dissert. Dorpat, 1867.

*Fries, E.*, Ueber die Fettresorption und die Entstehung der Becherzellen. Virchow’s Arch. 1867. Vol. XL, p. 519.

*Gerlach, L.*, Ueber den Auerbachschen Plexus mysentericus. Arbeiten aus d. physiol. Anstalt. Leipzig. 1872, pp. 102–112.

*Gonjaew, K.*, Die Nerven des Nahrungsschlauches. Arch. f. mik. Anat. 1875. Vol. XI, pp. 479–496.

*Gruby* and *Delafond*, Résultats des recherches faites sur l’anatomie et les fonctions des villosités intestinales, etc. Compt. rend. 1843. Vol. XVI, p. 1194.

*Grugenhagen, A.*, Ueber Fettresorption und Darmepithel. Arch. f. mik. Anat. 1887. Vol. XXIX, p. 139.

*Heidenhain, R.*, Die Absorptionswege des Fettes. Moleschott’s Untersuchungen. 1858. Vol. IV, p. 251.

*Henle, J.*, Symbolae ad anatomiam villorum intestinalium impr. eorum epithelii et vasorum lacteorum. Berolini, 1837.

*Hoffmann, C. K.*, Bronn’s Klassen und Ordnungen des Thierreichs. Leipzig und Heidelberg, 1873–1878. Vol. VI, pp. 412–424.

*Klein, E.*, Der Darmkanal in Stricker’s Gewebelehre, Article XVI.

*Klein, E.*, Contributions to the anatomy of Auerbach’s Plexus in the intestine of the frog and toad. Quart. Journ. Micros. Sci. 1873. Vol. XIII, p. 377.

*Klein, E.*, and *Verson, E.*, Der Darmcanal, in Stricker’s Gewebelehre, 1871, p. 355.

*Klein, E.*, Der neue Nervenapparat v. Thanhoffer’s. Centralbl. f. d. med. Wiss. 1883, p. 82.

*v. Kölliker, A.*, Nachweis eines besonderen Baues der Cylinderzellen des Dünndarms. Verhandl. d. phys.-med. Gesells. Würzburg, 1856. Vol. VI, p. 153.

*v. Kölliker, A.*, Handbuch der Gewebelehre.

*Lambl*, Ueber die Epithelialzellen der Dünndarmschleimhaut. Wiener med. Wochenschr. 1859. Nos. 24 and 25.

*Langer, C.*, Ueber das Lymphgefässsystem des Frosches. Wiener Acad. Sitzungsb. 1866. Vol. LIII, Pt. I, p. 395.

*Letzerich, L.*, Ueber die Resorption der verdauten Nährstoffe im Dünndarm. Virchow’s Archiv. 1866, Vol. XXXVII, p. 232; 1867, Vol. XXXIX, p. 435.

*Lipsky, A.*, Beitrag zur Kenntniss des feineren Baues des Darmcanals. Wiener Akad. Sitzungsb. 1865. Vol. LV, Pt. I, p. 183.

*Oeffinger*, Einige Bemerkungen über die sogenannten Becherzellen. Arch. f. Anat. u. Physiol. 1867, p. 337.

*Partsch, C.*, Beiträge zur Kenntniss des Vorderdarmes einiger Amphibien und Reptilien. Arch. f. mik. Anat. 1877. Vol. XIV, p. 179.

*Remak, R.*, Ueber peripherische Ganglien an den Nerven des Nahrungsrohrs. Arch. f. Anat. u. Physiol. 1858, p. 189; also in Zeit. d. Vereins f. Heilkunde in Preussen. 1840.

*Renzoni*, Osservazioni e ricerche sul epitelio intestinale. Rendiconti dell Acad. di Napoli. 1868.

*Rusconi*, Riflessioni sopra il sistema linfatico dei rettili. Pavia, 1845.

*Sachs, J.*, Zur Kenntniss der sogenannten Vacuolen oder Becherzellen im Dünndarm. Virchow’s Arch. 1867. Vol. XXXIX, p. 493.

*Schultze, F. E.*, Das Drüsenepithel der schlauchförmigen Drüsen des Dünn- und Dickdarms und die Becherzellen. Centralbl. f. d. med. Wiss. 1866, p. 160.

*Schultze, F. E.*, Epithel- und Drüsen-Zellen. Arch. f. mik. Anat. 1867. Vol. III, p. 145.

*Thanhoffer, L.*, Beiträge zur Fettresorption und histologischen Structur der Dünndarmzotten. Pflüger’s Arch. f. d. ges. Physiol. 1874. Vol. VIII, pp. 391–443.

*v. Thanhoffer, L.*, Ein neuer Nervenapparat im Dünndarm. Centralbl. f. d. med. Wiss. 1883, p. 33.

*v. Thanhoffer, L.*, Antwort auf Herrn Prof. Klein’s ‘Der neue Nervenapparat etc.,’ betitelte Bemerkungen. Centralbl. f. d. med. Wiss. 1883, p. 176.

*Valatour, M. M.*, Recherches sur les glandes gastriques et sur les tuniques musculaires du tube digestif dans les poissons et les Batraciens. Annales des Sci. nat. 4th Series, Vol. XVI. Zool. 1861, pp. 219–285.

*Watney, H.*, The minute anatomy of the alimentary canal. Phil. Trans. 1877. Vol. CLXVI, Pt. II, p. 451.

*Wiegandt*, Untersuchungen über das Dünndarmepithel. Dissert. Dorpat, 1860.

*v. Wittich*, Beiträge zur Frage über Fettresorption. Virchow’s Arch. 1857. Vol. XI, p. 37.

THE LIVER, GALL-BLADDER, AND PANCREAS.

*Barfurth, D.*, Vergleichend-histochemische Untersuchungen über das Glycogen. Arch. f. mik. Anat. 1885. Vol. XXV, p. 369.

*Brotz, J.*, and *Wagenmann, C. A.*, De amphibiorum hepate et glandularum ductu excretio carentium structura deque earundem functionibus experimenta. Berolini, 1841.

*v. Brunn, A.*, Flimmerepithel in den Gallengängen des Frosches. Zool. Anzeiger. 1883. No. 148, p. 483.

*Eberth, C. J.*, Die Pigmentleber der Frösche und die Melanämie. Virchow’s Arch. 1867. Vol. XL, p. 305.

*Eberth, C. J.*, Zur Kenntniss der Verbreitung glatter Muskeln. Zeitschr. f. wiss. Zool. 1863. Vol. XII, p. 360.

*Eberth, C. J.*, Ueber den feineren Bau der Leber. Centralbl. f. d. med. Wiss. 1866, p. 897.

*Eberth, C. J.*, Untersuchungen über die Leber der Wirbelthiere. Arch. f. mik. Anat. 1867. Vol. III, p. 423.

*Eberth, C. J.*, Untersuchungen über die normale und pathologische Leber. Virchow’s Arch. 1867. Vol. XXXIX, p. 70.

*Eberth, C. J.*, Ueber die Pigmentleber der Frösche. Virchow’s Arch. 1862. Vol. XXIX, p. 70.

*Gerlach, L.*, Ueber die Nerven der Gallenblase. Centralbl. f. d. med. Wiss. 1873, p. 562.

*Hering, E.*, Ueber den Bau der Wirbelthierleber. Wiener Acad. Sitzungsb. 1886. Vol. LIV, Pt. I, p. 335.

*Hering, E.*, Ueber den Bau der Wirbelthierleber. Arch. f. mik. Anat. 1867. Vol. III, p. 88.

*Hering, E.*, On the liver. Stricker’s Gewebelehre. 1872, p. 429.

*Hoffmann, C. K.*, Bronn’s Klassen und Ordnungen des Thierreichs. Leipzig und Heidelberg, 1873–1878. Vol. VI, p. 424.

*Jones, C. H.*, On the structure and development of the liver. Phil. Trans. 1849. Pt. I, p. 122.

*Langley, J. N.*, On variations in the amount and distribution of fat in the liver-cells of the frog. Proc. Roy. Soc. 1886. Vol. XXXIX, p. 234.

*Leydig, F.*, Lehrbuch der Histologie. 1857.

*Leydig, F.*, Die Leber der Fische und Batrachier.

*Nussbaum, M.*, Ueber den Bau und die Thätigkeit der Drüsen (Pancreas). Arch. f. mik. Anat. 1877. Vol. XIII, p. 752.

*Popoff, M.*, The nerves of the gall-bladder (in Russian). Rudneff’s Journ. f. normal. u. pathol. Histol., etc. 1872.

*Remak, R.*, Ueber runde Blutgerinnsel und über pigmenthaltige Zellen. Arch. f. Anat. u. Physiol. 1852, p. 115.

*Weber, E. H.*, Ueber die periodische Farbenänderung welche die Leber der Hühner und Frösche erleidet. Bericht von Verhandl. K. Säch Gesell. Leipzig, 1850, p. 15.

*Zeller, A.*, Die Abscheidung des indig.-schwefelsauren Natrons in den Drüsen (Pancreas). Virchow’s Arch. 1878. Vol. LXXIII, p. 257.

THE SPLEEN.

*Billroth, T.*, Beiträge zur vergleichenden Anatomie der Milz. Arch. f. Anat. u. Physiol. 1857, p. 88.

*Billroth, T.*, Beiträge zur vergleichenden Anatomie der Milz. Virchow’s Arch. 1861, Vol. XX, p. 410, and 1862, Vol. XXIII, p. 457; also Zeitschr. f. wiss. Zool. 1862, Vol. XI, p. 325.

*Ecker*, Blutgefässdrüsen, in Wagner’s Handwörterbuch der Physiologie. 1849. Vol. IV.

*Gray, H.*, On the structure and use of the spleen. London, 1854.

*Hoffmann, C. K.*, Bronn’s Thierbuch. Leipzig und Heidelberg, 1873–1878. Vol. VI, p. 509.

*v. Kölliker, A.*, Ueber den Bau und die Verrichtungen der Milz. Mittheil. d. naturf. Gesell. in Zürich, 1847. Vol. I, p. 120.

*Kusnezoff, F.*, Ueber blutkörperchenhaltige Zellen der Milz. Wiener Sitzungsber. 1873. Vol. LXVII, Pt. III, pp. 58–67.

*Müller, W.*, Ueber den feineren Bau der Milz. Leipzig und Heidelberg, 1865.

*Remak, R.*, Ueber runde Blutgerinnsel und über pigmenthaltige Zellen. Arch. f. Anat. u. Physiol. 1852, p. 115.

*Schweigger-Seidel, F.*, Untersuchungen über die Milz. Virchow’s Arch. 1862. Vol. XXIII, p. 526.

*Stieda, L.*, Zur Histologie der Milz. Dorpat, 1862.

THE PERITONEUM.

*Alltmann, R.*, Ueber die Veränderungen des serösen Epithels am blosgelegten Froschmesenterium. Arch. f. mik. Anat. 1878. Vol. XVI, p. 111.

*Arnold, J.*, Ueber die Durchtrittsstellen der Wanderzellen durch entzündete seröse Häute. Virchow’s Arch. 1878. Vol. LXXIV, p. 245.

*Batelli, A.*, Dello addaltamento di alcune cellule endotiali nelle membrane serose. Lo Sperimentale. 1884, p. 132.

*Cyon*, Ueber die Nerven des Peritoneum. Bericht über d. Verhandl. d. Kön. Säch. Gesell. d. Wiss. z. Leipzig, 1868. Vol. XX, p. 119. Leipzig, 1869.

*Grunau, H.*, Ueber das Flimmerepithel auf dem Bauchfell des weiblichen Frosches und über den Eileiterbau desselben. Dissert. Königsberg, 1875.

*Hoffmann, C. K.*, Bronn’s Klassen und Ordnungen des Thierreichs. Leipzig und Heidelberg, 1873–1878. Vol. VI.

*Hoffmann, T.*, Die Lungen-Lymphgefässe der Rana temporaria. Dissert. Dorpat, 1875.

*Kapff*, Untersuchungen über das Ovarium und dessen Beziehungen zum Peritoneum. Arch. f. Anat. u. Physiol. 1872, p. 553.

*Klein, E.*, On Remak’s ciliated vesicles and corneous filaments of the peritoneum of the frog. Quart. Journ. Mic. Sci. New Series, 1872. Vol. XII, p. 43.

*Klein, E.*, On the peripheral distribution of non-medullated nerve-fibres (nerves of the peritoneum). Quart. Journ. Micros. Sci. 1872. Vol. XII, p. 32.

*Leydig*, Lehrbuch der Histologie. 1857, p. 325.

*Mayer*, Ueber die Flimmerbewegung. Froriep’s Notizen, 1836. Vol. XLVII, p. 179.

*Neumann, E.*, Die Beziehungen des Flimmerepithels der Bauchhöhle zum Eileiterepithel beim Frosch. Arch. f. mik. Anat. 1875. Vol. XI, pp. 354–377.

*Nicolsky, P.*, Ueber das Flimmerepithel beim Frosche. Centralbl. f. d. med. Wiss. 1880, p. 641.

*Paladino, G.*, Dell’ endotelio vibratile nei Mammiferi ed in generale di alcuni dati sulla fisiologia delle formazioni endoteliche. Estr. dal Giornale intern. delle Scienze Mediche. 1882. Vol. IV.

*Schweigger-Seidel* and *Dogiel*, Ueber die Peritonealhöhle der Frösche. Arbeiten aus d. physiol. Anstalt zu Leipzig. 1866, p. 68.

*Solger, B.*, Ueber einige Entwicklungsstadien des Peritonealepithels der Amphibien-larven. Manusc. d. Naturf. Versamml. zu Freiburg. 1884.

*Thiry*, Ueber das Vorkommen eines Flimmerepitheliums auf dem Bauchfell des weiblichen Frosches. Göttinger Nachrichten. 1862, pp. 171–174.

*Tourneux*, Recherches sur l’épithelium des sereuses. Journ. de l’anat. et de la physiol. 1874.

*Waldeyer*, Eierstock und Ei. Leipzig, 1870, pp. 72 and 122.

*Wolff, W.*, Ueber freie sensible Nervenendigungen. Arch. f. mik. Anat. 1882. Vol. XX, pp. 377–381.

THE ALIMENTARY TRACT, ETC.

I. THE ALIMENTARY TRACT.

The alimentary tract consists of the mouth or pharyngo-oral cavity, the oesophagus, the stomach, the small intestine and the large intestine; these together forming a tube extending from the mouth to the cloaca. From the commencement of the oesophagus, at the entrance to the larynx, to the end of the cloaca, the length of the tube is about 31.5 cm., that of the various parts being:

From glottis to pylorus 5.5 cm. From pylorus to large intestine 22.0 cm. Large intestine to end of cloaca 4.0 cm. -------- Total length 31.5 cm. ========

A. The *Mouth*.

The mucous membrane covering the tongue will be described with the sense-organs (see organ of taste).

*a.* *General description.* The mouth of R. esculenta, as in all other amphibia, with the exception of the lowest (Siren, Proteus, etc.), is of considerable width, and extends backwards as far as the middle of the tympanic membrane. The upper margin of the mouth possesses a lip or fold of the skin (SS^{1}), which projects sufficiently to prevent the teeth being seen from the front or from the sides. This lip-like rim is most prominent in the premaxillary and superior maxillary regions, but can be traced along the whole length of the upper jaw, and on to the lower jaw, by means of a well-marked fold at the angle of the mouth. Beyond this point the lip is absent, as the skin is closely attached to the bony mandible.

On the *roof* of the *mouth* the following structures can be made out: immediately within the lip is a deep, well-marked groove, the outer boundary formed by the lip, the inner by a fold of the mucous membrane (Fig. 178 F); this fold increases from behind forwards as far as the premaxillary bones, where it forms two prominences (F^1, F^1) with an interval between. These correspond to the palatine processes of the premaxillary bones: immediately behind them are openings of the ducts of the intermaxillary glands. In the groove so formed are placed a single row of simple teeth, which, though subject to many variations, are usually about fifty in number.

The roof of the mouth.

Cho Posterior naris. ID Opening of intermaxillary glands. F Fold of mucous membrane. F^1, F^1 Prominences of mucous membrane. K Muscles. O Floor of the orbit. S Lip. S^1 Lip. T Eustachian tubes. Vo Vomer. ]

A little further back and to either side of the median line is a small group of vomerine teeth (Vo); each group has from five to ten teeth; external to these is on each side a transversely-placed oval opening, the posterior nares (Cho). These apertures are directed outwards and backwards into a shallow groove, bounded anteriorly by a fold of mucous membrane.

According to Wiedersheim the mucous membrane immediately around the vomerine teeth is supplied with taste-bulbs; the epithelium surrounding these being non-ciliated.

The roof of the mouth underneath the parasphenoid is somewhat vaulted and on either side depressed by the eyeballs, which project downwards more or less prominently (O, O). Still further back are the openings of the Eustachian tubes (Fig. 178 T), one on each side, and almost surrounded by the limbs of the pterygoid bones.

On the *floor* of the *mouth* (Fig. 179) the tongue (Z, Z^1) forms the most prominent object; its shape varying according to the state of contraction of its muscles. Behind it, in the middle line, is a transverse groove (†), corresponding to the posterior border of the hyoid bone, and still further back is the opening to the larynx (L), a longitudinal slit about 3 mm. in length. The mucous membrane to either side of the tongue is only slightly folded, and a little in front of the angle of the mouth is depressed into an aperture (S), opening into the vocal sac. This opening is surrounded by small radiating folds of mucous membrane, and is oval in shape.

The floor of the mouth.

K Muscles. L Opening to larynx. M Mandible. S Opening to voice-sac (in males only) Sm Chin. Z Tongue. Z^1 Left cornu of bifid tongue. † Folds opposite hinder border of the hyoid. ]

Towards the oesophagus the mucous membrane of both the roof and the floor of the mouth is thrown into numerous longitudinal folds.

*b.* The *minute structure* of the several parts.

(1) The *mucous membrane* of the mouth. At the junction of the skin and the mucous membrane there is a gradual transition from the stratified epithelium of the skin to a single layer of *columnar epithelium*. On the floor of the mouth this condition is reached at the tongue; on the roof the transition takes place more quickly. The columnar epithelium of the mouth (that of the tongue is excluded from this description) is ciliated; scattered cells, which are not ciliated, are found here and there irregularly, but are not numerous. The cylindrical cells are very finely granular in their upper parts, clearer in the middle portion, more coarsely and darkly granular in their deeper portions; each cell is possessed of a large, well-defined, oval nucleus, which contains one or sometimes two nucleoli. The non-ciliated cells usually present a sharply differentiated, structureless, hyaline, free border (Schultze). The epithelium towards the margin of the mouth, where it is stratified, is also ciliated.

Goblet-cells occur in every part of the epithelium, whether ciliated or non-ciliated, and their forms vary very greatly.

(2) The *teeth* are wanting in the lower jaw; on the roof of the mouth they are found in two situations: as a single row in the groove within the lip, and a group on each vomer. Each tooth has the form of an elongated cone, which in the case of the jaw-teeth is curved, in that of the vomerine teeth straight. The teeth are fixed to the jaw so as to project upwards and slightly inwards, those at the front of the mouth projecting backwards, and those on the vomers project backwards. Each tooth has a small, sharp projection, or secondary crown on its outer surface (Fig. 181), placed near the mucous membrane. The teeth are fixed to the bones by means of Crusta petrosa, which is again united to the bones of the mandible by a matrix of spongy bone, continuous for the several teeth. Between the tooth and the mucous membrane is a layer of flattened epithelium (II), which extends more deeply on the inner side of the tooth than on the outer; the layer is continuous with the epithelium of the mouth, and is two to three cells in thickness. Each tooth has fine longitudinal grooves on the basal part of its outer surface, and consists of two parts, a crown and a root. The teeth possess large cavities, the wall being thin and almost of even thickness, except on the inner surface of the basal portion of the root, where the wall is wanting, and so forms a large aperture to the root.

The general skeleton of the tooth is formed of dentine, this is covered on the crown by a layer of enamel, and the Cuticula dentis on the socket by a layer of Crusta petrosa.

α. The *dentine* is a homogeneous substance pierced by numerous tubules (D), which arise at the pulp-cavity and course in a parallel direction to the surface of the dentine, where they form a rich network with irregular, interglomerular spaces. The inner surface of the dentine is rough, through the presence of numerous small, dark tubercles.

β. The *enamel* covers the dentine on the apical portion of the tooth. It has tubes coursing through it, which are continuous with those of the dentine, and presents also circumferential striations (Fig. 181 III).

I. Transverse section of the premaxillary bone to show attachment of the teeth; after Hertwig. Magnified 22 times.

II. Dentine and enamel; after Hertwig. Magnified 500 times.

III. Enamel: after Hertwig. Magnified 500 times.

A Blood-vessel of the pulp-cavity. C Crusta petrosa. D Dentine. F Processus dentalis. H Layer of epithelium. O Tooth cuticle. R Reserve. S Enamel. X Cutaneous glands. ]

γ. The *tooth cuticle* (Cuticula dentis) is colourless and covers the enamel. It is highly refractive, very transparent, and very resistant to chemical reagents. From the apex, towards the Crusta petrosa, it thins very rapidly, but is continued sufficiently far to cover a portion of the Crusta petrosa.

δ. The Crusta petrosa resembles bone, except that it contains no Haversian canals; it possesses cells which resemble bone corpuscles, and are usually somewhat rounded or oval and communicate with each other by their processes; for the most part it is homogeneous and free from cells (Hertwig).

ε. The *pulp-cavity* contains a connective-tissue very rich in cellular elements; those cells adjacent to the dentine are arranged in a layer (Membrana eboris) which has somewhat the appearance of a layer of epithelium. The cells (odontoblasts) of this layer are spindle-shaped, and send processes (dentinal fibres) into the dentinal tubules. A small blood-vessel can be traced into each cavity, but as yet no nerve has been found in the pulp-cavities.

(3) The *intermaxillary glands* (Glandula intermaxillaris) consist of a mass of convoluted tubes, lying chiefly between the premaxillary bones and the capsule of the nose, and opening by about twenty to twenty-five ducts at the fore-part of the mouth (Fig. 178 ID). A portion of the glands extends high into the nasal cavity (Born), while dorsally another portion lies under the skin and the M. dilatator and M. lateralis narium, which together act as compressors to the subjacent glands: a small, elastic, cartilaginous rod, placed between the anterior margin of the nasal capsule and the under surface of the ascending limb of the premaxilla, opposes these muscles on either side by its spring-like action (Wiedersheim).

In a fresh skull the openings of the ducts can easily be seen after washing away the mucous secretion; they are, however, seen to better advantage by treatment with Müller’s fluid and subsequent staining with carmine. With sufficient magnifying power, they are then seen as a row of bright dots. The tubules are of uniform thickness, placed closely side by side, and surrounded by a nervous plexus, which contains numerous branching nerve-cells. The epithelium of the tubules is cylindrical, with a rounded, finely granular nucleus; processes from the peripheral ends of the cells are continued to a Membrana propria. The ducts are lined with columnar, ciliated epithelium.

The *secretion* of the glands is remarkably adhesive, and is wiped off by the tongue when it is projected; by this means the tongue becomes a particularly efficacious instrument for capturing prey. The glands are, both histologically and chemically, pure mucous glands. In urodeles the homologous glands are placed in the hollow septum of the nose, between the nasal cavities.

(4) The *tongue* (Figs. 179, 182, 183) is a broad, fleshy flap on the floor of the mouth, to which it is attached by the anterior half of its ventral surface as far forwards as the chin. Seen from above it has a wedge-like form, being narrow in front and wider behind, where it is prolonged at each angle to form two cornua.

By raising the tongue one obtains a view of a portion of the M. hyoglossus. The two MM. hyoglossi arise (see page 66) some distance apart, and run forwards and towards each other to meet on the ventral surface of the hyoid bone; they now assume a longitudinal direction, and course forwards parallel to each other until they reach the M. genio-glossus (Fig. 182 G). Each muscle now divides to form coarse bundles, which ascend on either side of the M. genio-glossus towards the dorsum of the tongue. In this course they are encircled by a strong, elastic, connective-tissue sheath. The sheath is incomplete at the hinder end of the M. genio-glossus, where it possesses rounded apertures, through which the glossopharyngeal nerves (N, N) disappear, to be distributed, after a sharp curve backwards, in the substance of the organ.

The M. genio-glossus arises, in two parts on either side, at the side of the chin. One part (Fig. 182 G) is dorsal and median, the other (Fig. 182 G^1) ventral and external.

Muscles of the tongue, seen from the ventral surface.

G Median portion of M. genio-glossus. G^1 Lateral portion of M. genio-glossus. H Hyoid. Hy M. hyoglossus. L Larynx. M Mandible. N Glossopharyngeal nerve. ]

The first part, with its fellow of the opposite side, forms an arched commissure in the form of muscular rings, which decrease in size from before backwards, and so form a pear-shaped mass: the second, external portion, extends backwards, with a slight obliquity, as a thin, fan-like expansion, to the mucous membrane, where it is inserted. This arrangement can easily be seen after dissecting away the sheath (Fig. 183 Hy); the hindermost fibres curve sharply into the tongue (Hy^1); the anterior fibres pass obliquely forwards and blend with the straight fibres of the dorsal portion of the M. genio-glossus (Fig. 183 Gg). The arcuate fibres of the M. genio-glossus pass, for the most part, upwards and outwards to the tips of the posterior bifid border of the tongue; in this course they lie as a rule above the M. hyoglossus, but here and there the two muscles intermix (Fig. 183 Gg^1), and it is by no means easy to separate them.

The M. hyoglossus is the retractor of the tongue, the M. genio-glossus the protractor.

(For mucous membrane of the tongue, see organ of taste. The vocal sacs are described with the organs of voice and respiration.)

B. The *Oesophagus* and *Stomach* (Figs. 184, 185, 189, 194, 195, 199).

*a.* *General description.* The oesophagus is not separated from the pharyngo-oral cavity by a sharp line of demarcation. It has a length of only a few mm. in medium-sized frogs (Fig. 184 Oe), and lies in the middle line of the body, supported on either side by the cornua of the hyoid bone. The oesophagus lies on the dorsal wall of the larynx, is smooth externally, and is thrown into well-marked longitudinal folds internally.

Muscles of the tongue, from the ventral surface.

G M. genio-glossus. Gg Straight fibres of the M. genio-glossus. Gg^1 Curved fibres of the M. genio-glossus. Hy and Hy^1 M. hyoglossus. Z Borders of the tongue. ]

The transition from oesophagus to stomach is somewhat indefinitely marked by a slight dilatation of the tube, often scarcely perceptible, still it can always be recognized by an abrupt curvature to the left (Fig. 184 M), which becomes more prominent when the stomach is distended. Externally the stomach is seen as an elongated, slightly curved cone, smooth externally and of equal diameter throughout.

The oesophagus and stomach are held in position by folds of peritoneum (mesentery), which attaches them to the dorsal wall of the abdominal cavity, to the lungs, pericardium, and liver; and by the blood-vessels.

*b.* *Minute structure.* The walls of these viscera are composed of four layers or coats.

(1) The *serous coat* (Fig. 186) is a layer of endothelium, lying on a very thin stratum of connective-tissue; the whole derived from the peritoneum, which encloses the organs.

(2) The *muscular coat* (Fig. 186 LM and TM) is arranged in two layers, one (LM) longitudinal, the other (TM) transverse. The longitudinal layer is thicker in the oesophagus, and thins as it is continued to the pyloric end of the stomach. The circular layer, on the other hand, gains in thickness; both layers are of unstriated muscular fibre.

The alimentary canal.

A Opening of large intestine into cloaca. Cl Cloaca. D Small intestine. Du Duodenum. HB Urinary bladder. M Stomach. Mz Spleen. Oe Oesophagus. Py Pylorus. R Large intestine (rectum). † Junction of small and large intestine. ]

(3) The *submucous coat* (Fig. 186 A, B, and SM) is better developed in the stomach than in any other part of the alimentary canal. It is formed of a wide-meshed, loose connective-tissue, which supports numerous blood-vessels and lymphatics. Towards the mucous coat it possesses a well-differentiated Muscularis mucosa, which is arranged in two layers, a longitudinal (B) and a transverse (A).

(4) The *mucous coat* is possessed of numerous tubular glands, which vary in structure according to the part of the membrane examined. They have been the subject of much investigation (Heidenhain, Nussbaum, Partsch, Langley, and others), and are best described in three groups: those of the oesophagus, of the first part of the stomach, and of the pyloric end of the stomach respectively; between each pair of groups are transitional forms.

α. [The oesophageal glands are complete tubular glands lined by a single layer of epithelium, which very closely resemble the glandular cells of the fundus of the stomach (Plate II, Fig. 187). The cells are conical or cylindrical, the protoplasmic contents granular, the granules being larger than those of the corresponding cells in the stomach (Langley). Mucous cells are found among the true secretory cells. The cells of the ducts are sometimes, but rarely, ciliated (Langley).]

The abdominal viscera of Rana esculenta (female).

D Small intestine. Du Duodenum. EE Ovaries. H Heart. HB Urinary bladder. L Left lobe of liver. L^1 Right lobe of liver. L^2 Middle lobe of liver. Lg Left lung. Lg^1 Right lung. M Stomach. ]

β. [The glands of the fundus of the stomach are not so complex as the typical glands of the oesophagus. The cells at the mouth of the gland are continued into fine processes (Fig. 187), and their outer parts contain mucigen. The cells of the neck of the gland are more cubical, and towards the lower part of the neck are mucous cells. The cells of the body of the gland are of irregular shape, and so placed that the nucleus of one cell faces the junction of two cells on the opposite side (Langley). These cells are very finely granular.]

Transverse section through one of the longitudinal folds of stomach of Rana temporaria. To show general arrangement of the walls.--G. H.

A Transverse layer of muscularis mucosae. B Longitudinal layer of muscularis mucosae. LM Longitudinal muscular coat. M Mucous membrane. SM Submucous coat. TM Transverse muscular coat. ]

γ. [The glands of the pyloric end of the stomach have been compared with the mouths and necks of the glands of the fundus (Partsch, Langley). The cells are of two kinds only (Fig. 188). The cylindrical cells of the surface of the stomach are continued into the gland, where they become shorter and sub-cubical; these form the greater part of the gland. The cells at the deepest portion of the gland are more rounded, and resemble the mucous cells in the neck of the glands of the fundus.]

δ. [Between these well-marked groups of glands are various transitional forms. The transition from oesophageal to gastric glands is not a continuous one, as glands resembling those of the stomach can be found nearer the oesophagus than other glands, which more nearly resemble oesophageal glands. At the same point the mucous membrane is thinner than either in front or behind. In the same way an intermediate zone exists between the typical glands of the fundus and pylorus of the stomach.]

In both oesophagus and stomach the mucous membrane is thrown into longitudinal folds when the organs are empty. The epithelium of the surface of the oesophagus is mostly ciliated, and possesses numerous goblet-cells; according to Klein the cells are not set vertically on the subjacent submucosa, but obliquely.

Transverse section through the mucous membrane of the pyloric end of the stomach of Rana esculenta. After Partsch. (Obj. II, Syst. 7, Hartnack.) ]

(5) [The *nerves* of these organs, according to Gonjaew, contain both medullated and non-medullated fibres, which have nerve-cells attached to them. From these fine branches pass, either with the blood-vessels or alone, to the mucous coat, losing their medulla on the way. In this course they inosculate very freely, and are then distributed as very fine, beaded fibrils to the glands and epithelium, which are very richly supplied.]

(6) [The *blood-vessels* and *lymphatics* very closely resemble the corresponding structures in the small intestine (p. 290); the blood-vessels form a rich anastomosis in the submucous membrane; the lymphatics are arranged in two systems, one under the serous coat, and a larger system in the mucous and submucous coats. The oesophagus lies free in a peri-oesophageal lymph-sac (Robinson).]

C. The *Small Intestine*.

*a. General description.* The small intestine commences behind the middle of the abdomen at the pyloric end of the stomach, from which it is marked off by a slight constriction. The first portion of the small intestine is the duodenum (Figs. 184 and 194 Du); by means of an abrupt turn it winds directly forwards, parallel to the long axis of the stomach; the pancreas is placed in the loop so formed.

The whole of this portion of the intestine, together with the greater part of the stomach, is, in the normal condition, under cover of the liver (Figs. 185, 194): while under the liver the intestine is firmly attached to the deep surface of that organ by a short but strong Ligamentum hepato-duodenale; it then turns suddenly backwards, increases in size, and by means of numerous convolutions occupies a considerable portion of the right half of the abdomen (Fig. 184 D). It is held in position by a well-developed mesentery.

*b.* *Minute structure.* Like other portions of the alimentary canal, the small intestine is formed of four layers:--

(1) The *serous coat* presents no peculiarities; it consists simply of a layer of endothelial cells, with a small amount of sub-endothelial connective-tissue.

(2) The *muscular coat* is in two layers, the outer longitudinal layer being very thin, the inner circular layer thick.

(3) The *submucous layer* resembles that of the stomach, but is not so thick; the muscularis mucosae is well developed and arranged, as in the stomach, in two layers.

(4) The *mucous coat* (Fig. 189) is thrown into folds, which differ in various parts of the tube.

The longitudinal folds of the stomach are compressed together towards the pyloric end of the stomach (a) and diminish in size; at the commencement of the duodenum they end abruptly (a^1), but without any indication of a valvular arrangement.

Immediately beyond the pylorus the mucous membrane is folded so as to form an irregular network of folds which inclose irregular alveoli; the folds are thicker on the concave surface of the duodenum, and form a longitudinal ridge (b); in this ridge the alveolar spaces are much smaller than those to either side. The irregular folding extends through two to three cm., when a more regular arrangement commences in the form of two adjacent series of transverse folds (c, c^1). Each fold is semi-lunar in shape, with the convexity attached to the wall of the tube and directed forwards, while the concave free border and pocket-like space enclosed are directed backwards.

The arrangement of these folds reminds one of the semi-lunar valves of the human heart, and probably one of their functions is to prevent the regurgitation of the chyme (Wiedersheim).

The corresponding valves of opposite sides meet at each end at an angle, the apex of which is directed away from the stomach. On these folds and between them are smaller, secondary folds, partly irregularly arranged, partly longitudinal (d d).

Towards the middle of the small intestine this valvular arrangement is lost, to be replaced by an irregular net-like folding; beyond this longitudinal folds arise, which proceed in a sinuous course towards the large intestine.

The whole mucous membrane, both on the folds and otherwise, is covered with a simple layer of columnar epithelium, which is continued into numerous simple follicles (glands of Lieberkühn) found throughout the mucous membrane of the small intestine. The cells are placed on a basement membrane, which rests on a thin layer of loose connective-tissue, intervening between the epithelial coat and the muscularis mucosae. The epithelial cells are intermixed with a large number of goblet-cells, and have between them fine processes from the connective-tissue corpuscles of the subjacent layer; many of these processes extend to or even beyond the free margin of the epithelial cells.

Mucous membrane of the pyloric end of the stomach and the duodenum.

a Mucous membrane of the stomach. a^1 Commencement of duodenum. b Duodenal mucous membrane arranged in irregular network. c } Semi-lunar folds of c^1} the mucous membrane. d Longitudinal folds of the mucous membrane. ]

The individual cells are columnar, possessed of a well-marked cell-wall, and have distinct, large, oval nuclei, containing one or more nucleoli. The protoplasmic contents are granular, and with proper treatment show a very distinct intracellular network. The free margins of the cells are sharply marked off from the cell-contents, and are more firmly attached to the corresponding portions of adjacent cells than the rest of the cell-wall. This margin has a longitudinal striation, which owing to the important function performed by this part of the intestine, namely, absorption of the fat, has been the subject of many important investigations.

1837. Henle first described the border as a thickened, highly refractive portion of the cell-wall.

1855. Kölliker and Funke, after independent research, described the longitudinal striation: Funke offered no explanation of the fact, while Kölliker considered it due to the presence of fine tubules. Later Funke gave a modified support to Kölliker’s view by admitting the presence of tubules around the circumferential part of the border.

1856. Donders gave a description corresponding with that of Henle.

1857. Brettauer and Steinach gave it as the result of their investigations that the border was composed of closely-applied fine rods: v. Wittich first showed that the borders of adjacent cells were more firmly attached than the rest of the cell; he admitted the presence of apertures, but considered the whole appearance to be due to post-mortem changes.

Welcker and Friedreich agreed with the views of Brettauer and Steinach, but traced the striation throughout the length of the cells, in fact traced the tubules to the connective-tissue below.

1858. In this year Heidenhain published his results; he held the striation to be due to the presence of fine rods, and was the first to show that processes of the connective-tissue corpuscles passed up between the epithelial cells; he found fat globules in the epithelial cells, in the connective-tissue, and in the lacteals.

Friedreich described the striation as continued through the whole length of the cells, and as due to tubules.

1859. Lambl denied the presence of the rods, and considered the whole phenomenon an optical appearance due to the cell-wall; in this view he was supported by Vlakovich of Padua and Amici of Florence.

1860. Wiegandt held the border to be an independent covering, and the striation to be due to folding or wrinkling.

Col. Balogh described the border as formed of rods, but denied that these existed except when brought about by the action of fats; in support of this view he showed that the striation was wanting when fat was absent.

1865. Lipsky held the border to be composed of rods.

1866. Henle described the cells as in his former work, but now held the border to be composed of rods, in fact to represent a ciliated border.

1867. Erdmann described the border as being of two layers, an upper, thicker layer, with both longitudinal and transverse striation, and a lower, thinner layer, the true cell-wall. The upper layer he described as capable of splitting in the directions of both striations.

Schultze described the border as not being in intimate connection with the protoplasm of the cell. Arnstein and Wiegandt supported Heidenhain’s description.

1868. Albini e Renzoni described the part as resembling resting cilia.

1869. Eimer traced fat-globules into all the parts, epithelium, connective-tissue, and vessels; and held that the fat could pass from a lacteal to a branch of the Vena porta.

1870. Heidenhain, after further investigation, supported his earlier views.

1874. Thanhoffer described the membrane as perforated, and the protoplasm of the cells as actively sending protoplasmic processes through these apertures; this he had seen in frogs in which all connection with the spinal nerves had been severed.

1875. Benjamins could not find the striation to be a constant occurrence, and failed to find the processes described by Thanhoffer.

1876. Krause found rod-like bodies round the margin of the border.

1877. Fortunatow supported Thanhoffer’s view.

1881. Landois observed appearances in Spelerpes fuscus, which led him to support Thanhoffer’s views.

1883. Wiedersheim supported Thanhoffer’s views.

1884. Wiemer supported Thanhoffer’s observations.

1888. Paneth failed to find any contractile protoplasmic processes, and asserts that the circumference of the border, when examined under certain conditions, is composed of rods.

From the same causes the goblet- or chalice-cells, already mentioned, have been the subject of much speculation and investigation.

1846. Frerichs drew and described these cells as empty cells.

In 1848 these cells were first described as epithelium capitatum by Gruby and Delafond.

In 1856 Donders described the cells as being open, and as discharging their contents into the canal; the cell-walls being then pressed together by the neighbouring cells, and the cell-contents being then gradually reformed.

In the same year Kölliker published results closely agreeing with those of Donders, and he traced the various stages of the process.

1857. Brettauer and Steinach held them to be cells which had lost their contents, and as the ‘cuticular border’ was absent, concluded that the cell-contents were in closer connection with the ‘border’ than with the rest of the cell-wall.

1865. Lipsky and Sachs both doubted the presence of such cells, and considered them due to the action of reagents or post-mortem change.

1866. Letzerich described the cells as open, and regarded them as the commencement of the lacteal system, while Dönitz thought the whole appearance due to reagents.

1867. Schultze and Eimer, independently, described them as unicellular glands. Erdmann, however, again denied their occurrence under normal conditions.

Oeffinger held the goblet-cells to be modified ordinary cylindrical epithelium cells; in which view he was supported by Arnstein.

1868. Schultze and Eimer, after renewed investigations, reiterated their former opinions.

1869. Eimer described the goblet-cells as secreting mucin, and as capable, by division, of throwing out pus-like cells.

1876. Krause described the cells as containing granular contents, which under certain conditions are thrown out.

1877. Tolldt considered them artificial productions. Edinger asserted that they are formed from the cylindrical cells.

1877–1885. Partsch (1877), Klein and Hebold (1879), Stöhr (1880), Patzelt (1882), Haller (1883), Holl (1885), support the last view.

1878. Hoffmann supported Schultze’s views.

1886. List describes these organs as unicellular mucous glands.

1887. Paneth described them as secreting mucous and as being derived from the cylindrical cells.]

(5) [The *blood-vessels* of the small intestine (p. 234) have been described by Langer; he finds the vessels arranged in networks, one a subserous network, placed underneath the serous coat, and formed of elongated, irregular, four-cornered meshes. When the intestine is distended the meshes are rectangular.

The vessels to the mucous membrane divide and anastomose very freely in the submucous layer, and then form an irregular network on the inner surface of the Muscularis mucosa; this network follows all the foldings of the mucous membrane, and thereby supplies a double layer to each villous fold of the mucous membrane. The meshes are usually four-sided or five-sided.]

(6) [The *lymphatics* of the small intestine (Figs. 190, 191). The lymphatic vessels on reaching the intestine usually bifurcate; the two branches, as a rule, follow and enclose an arterial twig. From the serous layer they receive the contents of a very fine lymphatic plexus, the lumens of which are slightly greater than that of the corresponding capillaries; from the mucous layer they receive the contents of the lacteals: between these two layers the lymphatics anastomose very freely by means of numerous branches (Langer).

The lacteals are lined with an epithelioid layer and traversed by connective-tissue trabeculae, which have a like covering. The lacteals are not simple but in the form of a coarse network (Fig. 189) (Langer).]

Isolated fold of mucous membrane of small intestine of Rana temporaria; after Langer. Forty times natural size. Blood-vessels striped, lacteals shaded. ]

(7) [The *nerves* of the small intestine (p. 200) usually follow the arteries to the muscular coats, between which they form a plexus (Auerbach’s plexus); from this numerous twigs are given off, which course alone or in company with vessels to the mucous coat, where a second plexus (Meissner’s plexus) is formed. Auerbach’s plexus, according to Klein, consists of bands of nervous fibrils in endothelial sheaths; they branch and inosculate, and thus form a plexus. Where several such branches meet, a more or less complicated decussation of the bands of fibres takes place. Along these nervous bands are ganglion cells, either isolated or in groups. The cells are large, generally spherical, and contain a sharply outlined nucleus with a single or double nucleolus. The smaller cells generally appear to possess only one process, which can be traced from the protoplasm of the cell between the fibrils of the nerve-trunk. The larger cells are distinctly multipolar, their protoplasm being provided with a number of fine processes, or, as is oftener the case, with one large and several small processes. In many instances Klein was able to distinguish around the ganglion-cells a capsule of a spherical or ovoid shape. In these cases the body, as well as the processes of the ganglion-cell, were lying within the capsule. This system of ganglion-cells is in connection with the individual bundles within the nerve-trunks.

Transverse section of a fold of the mucous membrane of Rana temporaria; after Langer. Sixty times natural size.

A Lacteals with transverse trabeculae. B Circular muscular layer. C Longitudinal muscular layer. Blood-vessels striped. ]

Klein describes a second system of ganglion-cells, situated in meshes, which are formed by the nerve-trunks of the plexus itself. These ganglion-cells are much larger than the former, and are multipolar; their protoplasm, which is distinctly fibrillar, with granules between the fibrils, is provided with one or two long, thick processes and several short and thin ones; generally the processes are branched. The general shape of the cells is oblong, the thick, long processes being commonly at the two opposite poles. The cells are generally isolated, sometimes situated in the centre of a mesh, or more commonly near a nerve-trunk that borders the mesh on one side. Each ganglion-cell is connected with a nerve-trunk of the plexus by at least one process. In a few of the nerve-trunks of the general plexus, isolated medullated nerve-fibrils are seen to pursue an almost straight course from one trunk into another and divide into two. There is no connection between these medullated fibres and the ganglion-cells.

*Auerbach’s plexus* is a much finer plexus than that just described, and the ganglia are much smaller. It supplies twigs to the Muscularis mucosa; these break up into fine fibrils, which follow the direction of the muscle-fibres; other twigs supply the blood-vessels, with which they can be traced into the bases of the folds of mucous membrane. Thanhoffer has recently (l. c.) described nerve-fibrils, which terminate in the mucous epithelium.]

D. The Large Intestine (Fig. 184 R).

From a transverse section of the large intestine of Rana temporaria, moderately distended.--G. H.

A Denser portion of submucous coat. B Looser portion of submucous coat. C Artery, cut obliquely. D Circular muscle-layer. E Longitudinal muscle-layer. ]

*a.* *General description.* The large intestine is a flask-shaped viscus, lying in the median line. The small intestine opens into it by an abrupt curve at its anterior end. The large intestine is the widest part of the alimentary canal, is thin-walled, and diminishes in width towards its hinder end, where it opens into the cloaca above the opening of the bladder.

*b.* [*Minute structure.*

(1) The *serous coat* resembles that of the small intestine, etc.

(2) The *muscular coats* resemble those of the small intestine, but are thinner; the longitudinal layer is, however, proportionally thicker (Wiedersheim).

(3) The *submucous coat* (Fig. 192) resembles that of the small intestine in its general structure; the portion lying immediately beneath the mucous membrane (B) is denser in structure.

This layer has no Muscularis mucosa.

(4) The *mucous coat* (A) is a simple layer of large, columnar, epithelial cells, with large oval nuclei. The cells have a hyaline free border, but this possesses no striation. The mucous membrane is usually described as possessing numerous simple follicles (glands of Lieberkühn); in those specimens which I have examined they have been entirely absent (Figs. 192, 193). At six to eight points in a transverse section of a rectum moderately distended the submucous coat is thinner, and so throws the mucous coat into slight, longitudinal grooves; but these do not in the least resemble the glands of Lieberkühn.

Transverse section of large intestine of Rana esculenta; the mucous membrane thrown into longitudinal folds in consequence of the organ being contracted. Arteries injected with carmine.--G. H.

A Large circular vessels within the muscular coats. B Fine anastomosis to the mucous coat. ]

(5) The epithelium possesses goblet- or chalice-cells (Hoffmann), the number of which probably depends upon the period of the year and the state of digestion. In the rectum, from which the section for the figures 192 and 193 were cut, not one goblet-cell was found in a complete series of sections.

If the rectum be contracted, the mucous membrane is thrown into longitudinal folds.

(6) The *blood-vessels* (Fig. 193) have a simple arrangement. The arteries are large, and form oblique loops around the intestine, lying under the peritoneum; from these branches are given off to form a series of rings in the submucous membrane (Fig. 193 A); from these fine twigs are given off to form a fine anastomosis under the mucous membrane (B).

(7) The *lymphatics* of the large intestine are arranged in two chief systems: one under the serous coat resembles the corresponding system of the small intestine. The second set forms a network of rounded loops in the submucous coat, which give rise to a secondary set of smaller vessels towards the mucous membrane; this secondary system forms a sort of trellis-work standing on the rounded loops, and so maps out small blocks of the thick submucous coat. Towards the cloaca the arrangement is simpler; the secondary lymphatics are lost, while the primary lymphatics tend to form elongated, longitudinal loops (Langer).]

II. THE GLANDS CONNECTED WITH THE INTESTINAL CANAL.

A. The *Liver* and *Gall-bladder*.

*a.* *External form.*

(1) The liver (Figs. 185, 194) is a large, reddish-brown organ, occupying a large part of the anterior abdominal region. It consists of three or more lobes, which present many individual variations; as a rule there are two larger lateral lobes (L and L^1), and a smaller median lobe (L^2). Each lobe has a superficial or ventral surface, which is convex, and a deep or dorsal surface, which is concave and directed towards the other abdominal viscera lying above the liver. The two surfaces of each lobe meet to form a sharp border around the lobe, except where the three lobes are more intimately attached, opposite the apex of the heart (Figs. 185, 194); at this place each lobe possesses a small, flat, or slightly concave anterior surface.

The left lobe (L) hides the greater portion of the stomach, and has near its inner border a deep fissure, which runs forwards and so marks off a more or less well-marked fourth lobe. The anterior portion of the left lobe is attached to the corresponding portion of the right lobe by a narrow commissure.

The liver, seen from the ventral surface.

Du Duodenum. H Heart. L Left lobe of liver. L^1 Right lobe of liver. L^2 Middle lobe of liver. M Stomach. ]

The median lobe (L^2) extends backwards as far as the pylorus, and covers the commencement of the intestine together with the pancreas; these organs can, therefore, not be seen until this lobe is displaced. A fifth lobe is sometimes found on the dorsal surface of the median lobe, and to it or to the dorsal surface of the median lobe the small intestine is attached by the Ligamentum hepato-duodenale (Fig. 195 Lhp). The Vena portarum enters the liver behind this ligament.

The right lobe extends much further dorsalwards than the left lobe, and even comes in contact with the lung, the vessels of which sometimes indent its surface in spirit specimens. This lobe is also in contact with the base of the fat-body, and in females with the oviduct.

By drawing the lobes of the liver to either side and displacing the heart towards the head, the posterior caval vein is seen passing from the liver to the heart, and the hepatic commissure joining the lateral lobes is brought into view.

(2) The *gall-bladder* (Fig. 195 G) is placed on the dorsal surface of the liver in the deep niche between the right and left lobes; it is attached to the liver by connective-tissue and peritoneum.

The gall-bladder is round or oval in form; when moderately full it has a smooth, outer wall, which is thin and allows the green colour of the bile to be seen. It possesses a duct (Dcy), the cystic duct (Ductus cysticus), which bifurcates near its origin.

The two cystic ducts (Fig. 195 Dcy) join the larger hepatic ducts, as shown in the figure, and so form a simple anastomosis, from which three branches (3) of varying size unite at the anterior extremity of the pancreas to form the common bile-duct (Ductus choledochus, Dc). The common bile-duct runs through the whole length of the pancreas, receiving near its origin additional hepatic ducts (Dh^1) from the middle lobe of the liver. In this course the duct lies either on the ventral surface of the pancreas or under a thin layer of the glandular tissue; it receives the ducts of the pancreas and leaves that organ at its posterior border as a round and strong canal (Dc^1). The duct courses in the gastro-duodenal ligament, and reaches the dorsal surface of the duodenum at a very acute angle; it then pierces the wall obliquely and terminates with a slit-like or elongated oval opening.

The pancreas and bile-canals. The liver has been displaced towards the head.

Dc Common bile-duct. Dc^1 Common bile-duct after leaving the pancreas. Dc^2 Opening of the common bile-duct into the duodenum. Dcy Cystic ducts. Dh Hepatic ducts. Dh^1 Supplementary hepatic ducts from the middle lobe of the liver. Du Duodenum. G Gall-bladder. L Left lobe of the liver. L^1 Right lobe of the liver. L^2 Middle lobe of the liver. L^3 Fourth lobe of the liver. Lhp Gastro-hepatic ligament. M Stomach. P Pancreas. Py Pylorus. P^1 Ducts of the pancreas. ]

*b.* [*Minute structure.*

(1) The *liver* is composed of various tissues: it possesses a peritoneal covering, a fibrous covering, which supplies trabeculae to support the various other tissues, blood-vessels, hepatic cells or true liver parenchyma, and bile-canals.

α. The *peritoneal covering* of the liver encloses the organ almost completely, the only exceptions being where the various attachments of the liver are found (see peritoneum). The peritoneal covering of the liver is for the most part composed of flattened, ciliated cells (Neumann and Grunau); on the middle lobe these are, however, more or less replaced by non-ciliated cells. The thickness of these cells varies considerably, according to the amount of distension to which the liver is subjected.

β. The *fibrous covering* of the liver is very thin and very difficult to demonstrate; it consists of connective-tissue fibres with very few corpuscles. This covering is prolonged into the liver along the portal canals, where traces of connective-tissue can always be made out.

From these processes and from the whole of the inner surface of the general connective-tissue capsule are given off fine trabeculae, in which it is very difficult to find any nuclei; these trabeculae are everywhere extremely delicate and difficult to demonstrate; nowhere do they form distinct boundaries between lobuli: the structure closely resembles the sustentacular tissue of a lymphatic gland (Eberth).

γ. The *blood-vessels* to the liver are the portal vessels (p. 249) the hepatic veins (p. 247), and the hepatic artery (p. 233)

I. Partial injection of the liver from the portal vein (blue): Rana esculenta.--G. H.

II. Partial injection of the liver from the hepatic vein (red): Rana esculenta.--G. H.

III. Complete injection of the liver from the hepatic artery (red) and from the portal vein (blue): Rana esculenta.--G. H.

A Portal (interlobular) veins and their branches. B Hepatic (intralobular) veins and their branches. C Hepatic arteries and their branches. ]

(1) The portal vessels pass into the liver on its ventral surface; they divide into branches which course along the middle parts of each lobe and give off smaller branches in all directions towards the periphery; the interlobular branches (Fig. 196 I) forming a very complex capillary network. As compared with the hepatic veins (Fig. 196 II), the interlobular veins do not give off their capillaries so abruptly, but tend to supply these from small lateral branches. The portal veins are accompanied in their course by branches of the hepatic artery, and often by larger bile-ducts, and thus form portal canals. In no part do the portal (interlobular) veins or their branches limit the lobules by distinct rings of vessels, as seen in many higher animals. The interlobular veins and intralobular veins simply interdigitate with each other.

(2) The hepatic veins (Fig. 196 I and II) also course chiefly in the middle parts of the lobes of the liver; they branch, and ultimately supply intralobular veins which interdigitate with the interlobular veins (I and II). The capillaries arise very abruptly from an intralobular vein, and form a network of vessels communicating very freely with the corresponding capillaries of the interlobular veins.

(3) The hepatic arteries (Fig. 196 III) break up into small branches which, as a rule, course along the portal canal until near the surface of the liver, when they leave the portal veins and pass to the surface to supply the coverings of the liver. In their course along the portal canals they supply a few very small twigs to the structures forming the canals. At the surface of the liver the branches of the hepatic artery form capillaries, which empty themselves into the general capillary anastomosis beneath (Fig. 196 III).

δ. The *liver-cells* (Figs. 197, 198) are large, and of compressed spheroidal or polygonal shape. They possess no cell-wall, have usually one but sometimes two large nuclei, each with a distinct nucleolus. The cells often contain granules of glycogen or fat-globules. The main fibrillae of the intercellular network are arranged so as to extend between a bile-capillary and a blood-capillary (Fig. 197).

ε. The *bile-ducts* (Fig. 198) commence as fine tubes between the liver-cells, where they are simply small spaces enclosed by the hepatic cells; they are usually enclosed by three or four cells, possibly sometimes by only two cells (Hering). Such bile-capillaries are usually separated from a blood-capillary by the thickness of one liver-cell only (Fig. 198).

As a number of such bile-capillaries run together to form a larger duct, the cells enclosing them change their character, becoming flattened and broader; these cells may, however, be traced continuously into the true hepatic cells (Hering and Eberth). The bile-duct so formed then obtains a slight covering of fibrous tissue, which rapidly increases in quantity, courses along a portal canal, and receives other ducts on the way; the epithelium lining it gradually becomes more elongated, and ultimately resembles that found in the common bile-duct or the gall-bladder.

In the larger ducts the epithelium is, according to v. Brunn, ciliated; they also possess a layer of unstriated muscle-fibre (Eberth).]

Liver-cells, after Kupffer.]

ζ. The *pigment* of the liver varies very much in amount and character, according to the time of the year and state of health of the animal. According to Eberth the pigmentary masses are of about the same size as the white blood-corpuscles, and are possessed of the power of amoeboid movement (in young animals). The cells possess two to seven nuclei and vary much in colour and distribution. As a rule the larger the amount of pigment in a given liver the smaller is the number of fat-globules found in the individual liver-cells (Eberth).]

The bile-capillaries; natural injection with sulphindigotate of sodium: v v v represent blood-capillaries.--G. H.]

(2) [The *gall-bladder* and *bile-ducts*. The gall-bladder has four coverings.

α. A serous coat of peritoneal endothelium.

β. A muscular coat, containing unstriated muscle-fibres and connective-tissue.

γ. A sub-mucous coat of areolar-tissue.

δ. An internal lining of columnar epithelium.

ε. The walls of the gall-bladder are richly supplied with blood-vessels from the cystic arteries (p. 233); these form a close network in the submucous coat.

ζ. The muscular and submucous coats also possess a rich nervous plexus, which contains ganglia and resembles Auerbach’s plexus of the intestine (Popoff, Gerlach).]

B. The *Pancreas* (Fig. 199 P).

*a.* *General description.* The pancreas is a flattened, light yellowish-brown organ, placed in the loop of the duodenum between this latter and the stomach. The whole organ is within the gastro-duodenal ligament, and is attached to the liver; hence it is little influenced by changes in the amount of distension of the stomach or intestine.

The pancreas and bile-canals. The liver has been displaced towards the head.

Dc Common bile-duct. Dc^1 Common bile-duct after leaving the pancreas. Dc^2 Opening of the common bile-duct into the duodenum. Dcy Cystic ducts. Dh Hepatic ducts. Dh^1 Supplementary hepatic ducts from the middle lobe of the liver. Du Duodenum. G Gall-bladder. L Left lobe of the liver. L^1 Right lobe of the liver. L^2 Middle lobe of the liver. L^3 Fourth lobe of the liver. Lhp Gastro-hepatic ligament. M Stomach. P Pancreas. P^1 Ducts of the pancreas. Py Pylorus. ]

The organ may be completely exposed by either of two methods: in the former, the liver, stomach, and duodenum are drawn towards the head and the dorsal surface of the organ so exposed. In the second method the liver is drawn backwards, the various peritoneal folds which connect the duodenum with the posterior border of the liver cut through, and the three organs then separated; the pancreas can then be conveniently examined.

The size and shape of the pancreas are subject to great variations in different specimens. The usual shape of the organ is somewhat triangular (Fig. 199), the left border being usually unbroken, while the other two shorter borders are broken into lobes. The longest lobe stretches as far as the pylorus (Py), to which it is attached by connective-tissue: the opposite extremity of the gland is attached to the liver.

The excretory duct of the pancreas (Ductus Wirsurgianus) opens into the common bile-duct at about the middle of the pancreas (P^1); other smaller ducts may open into the same canal.

*b.* *Minute structure.* [The pancreas consists of a number of lobes loosely held together by connective-tissue; each lobe is composed of a number of lobules attached to each other much more intimately. The lobules are made up of tubes lined by a single layer of glandular epithelium. This epithelium is, as a rule, broadly columnar, but in the smaller tubes may be cubical or polygonal. Each cell has a cell-wall, nucleus, and very granular protoplasm; the latter shows two zones (in the inactive condition), a granular zone near the lumen, and an outer, clear, and finely striated zone (Nussbaum). The lumen of each alveolus is very small, and in many cases difficult to make out.

The smallest ducts have no special lining, and are therefore bounded by the glandular cells; the larger ducts have a flattened, cubical epithelium, which when seen from the surface has an appearance as if the individual cells were widely separated from one another; these ducts have a considerable layer of connective-tissue around them. The largest ducts are lined with a layer of columnar, ciliated epithelium; the cilia are very long, usually of about the same length as the cell, sometimes appearing to be even longer. This epithelium is continuous with the ciliated, epithelial layer of the common bile-duct, which it resembles. These largest ducts have an extremely thick layer of connective-tissue around them.

The pancreas and its ducts are very richly supplied with vessels and nerves; the nerves forming everywhere a fine plexus, the larger strands of which usually, but not always, course with the larger blood-vessels. The larger ducts have an especially rich supply of nerves, of which fibrils may be traced towards the ciliated epithelium; an anatomical connection between the two has not, however, been made out.]

III. THE SPLEEN.

*a.* *General description.* Although the spleen belongs to the lymphatic system, it is considered here in order to complete the description of the abdominal viscera. It is a small, rounded-oval body, of a reddish-brown colour, suspended in the mesentery near the anterior end of the large intestine (Fig. 184 Mz). In medium-sized animals the longer diameter is about 6 mm., and is parallel with the long axis of the body; the shorter diameter is about 5 mm., and the thickness varies from about 3 mm. to 4 mm. The dorsal surface is flat or slightly concave (Hilus lienis), and receives the relatively large afferent and efferent vessels; the rest of the organ is smooth and rounded, and with its greatest convexity directed towards the left side.

*b.* [*Minute structure.* The structure of the spleen resembles that of higher animals. It possesses a *serous coat* of peritoneum, under which is a *fibrous coat*; the latter sends in trabeculae, which divide and form a fine meshwork of supporting-tissue; the finest trabeculae are formed by the processes of the connective-cells of the sustentacular structure. According to Hoffmann, the thickness of the fibres averages 0.001 to 0.011 mm.; the intervening spaces measure 0.002 to 0.012 mm. The spaces are filled by the spleen pulp, which consists of true spleen-corpuscles, blood-corpuscles, and pigment-corpuscles.

The *spleen-corpuscles* have an average diameter of 0.006 mm., and are round or of a rounded oval form. Each consists of a nucleus, with a very small amount of adherent protoplasm; the nucleus possesses one or two nucleoli. Some of these cells contain a brownish or black pigment in granules, but most of them are colourless (Hoffmann).

The *pigment-cells* equal the white blood-corpuscles in size, and exactly resemble the corresponding pigment-cells of the liver.

The *blood-corpuscles* are found in various stages of disintegration and regeneration.

The *arteries*, on entering the spleen, at once break up into branches which pass in all directions, giving off twigs on all sides and at varying angles; from these capillaries are supplied, which traverse the parenchyma in all directions. The capillaries empty themselves partly into veins, partly into the splenic spaces.

The *veins* commence either as capillaries in connection with the arteries or by communicating with the splenic spaces. This communication is brought about by small twigs of about 0.015 mm. diameter, which have incomplete walls, and so open into the splenic spaces (Hoffmann).

*Malpighian bodies* are represented by collections of splenic cells on various arterial twigs; they are, however, not so sharply defined as is the case in some higher animals.]

IV. THE PERITONEUM.

*a.* *General description.* The *peritoneum* is a thin, pigmented membrane lining the abdominal cavity. Tracing it forwards from the ventral wall of the abdomen (Peritoneum parietale), it can be followed along the deeper surface of the muscles to the pericardium. The middle portion leaves the abdominal wall by accompanying the anterior abdominal vein; the lateral portions are continued further forwards, and then ascend on the pericardium and the deeper surfaces of the lateral walls in the thoracic region.

The peritoneum passes thence to the ventral surface of the liver (Ligamentum coronarium), covers this surface and passes on to the dorsal surface of the organ, which, together with the gall-bladder, it completely encloses. The membrane thus reaches the dorsal wall (Ligamentum suspensorium hepatis et pericardii); from the lateral borders of the liver it passes upwards to the dorsal wall, and thus forms a pocket-like pleuro-peritoneal cavity on either side.

From the dorsal wall and above the attachment of the coronary ligament of the bladder the peritoneum reaches the root of the lung on each side, and completely invests the organ: while in the middle line it covers the outer surface of the oesophagus and attaches it to the dorsal wall, thus forming the first part of the mesentery.

Just behind the root of the lung, the peritoneum, in female specimens, has an opening on each side (Ostium abdominale tubae Fallopiae), by which the oviduct communicates with the peritoneal cavity.

Tracing the peritoneum backwards, it passes over the ventral surface of the kidneys so as to exclude them from the peritoneal sac: in the middle line, between the kidneys, the peritoneum descends to form the mesentery for the small intestine. At the inner borders of the kidneys, the testes or ovaries are pushed into the abdominal sac, and so possess well-marked mesenteries; the mesovarium becomes longer towards the cloaca, but attains its greatest development in the breeding season, when it is arranged in numerous folds. Along the outer borders of the kidneys, in females, the peritoneum again descends into the abdominal cavities to enclose the oviducts, which have broad mesenteries. Towards the rectum these mesenteries are shorter and attached to either side of the bladder by a well-marked free border: as the middle line of the bladder is attached by the peritoneum to the rectum, two distinct pouches (Cava recto-vesicalia) are formed, which descend deeply into the pelvic cavity. The upper walls of these pouches are pushed in between the urostyle and the rectum, and together form a strong meso-rectum, which is longer near the Valvula Bauhinii and continuous with the mesentery of the small intestine. The hinder portion of this mesentery is very short, and only covers the lateral walls of the rectum.

With the exception of a small portion of its dorsal surface, which is attached to the rectum, the whole surface of the bladder is covered with peritoneum.

The mesentery of the alimentary canal commences in connection with the oesophagus between the roots of the lungs; it is attached to the dorsal surface of the liver, covering the posterior caval vein, and is attached to the gall-bladder. From this point it extends, as a free, arched fold, to the concave right border of the stomach, which is completely surrounded by peritoneum.

The gastro-duodenal fold (Ligamentum gastro-duodenale) extends from the stomach to the pylorus and includes the pancreas. The hepato-duodenal fold (Lig. hepato-duodenale) extends from the portal fissure of the liver to the duodenum.

The mesentery of the small intestine is broad and arranged in folds, which follow the curves of the intestine; and is attached in the middle line, immediately beneath the vertebrae, where it encloses the aorta.

The various folds and mesenteries carry the blood-vessels and nerves to the different organs; in this course the vessels are surrounded by large lymphatics, which communicate with each other.

Preparations from the peritoneum of Rana esculenta.--G. H.

I. From peritoneum of the ventral wall of abdomen, stained with silver and logwood (Hartnack, Oc. I, Syst. 7).

II. From mesentery of small intestine of Rana esculenta, stained with silver (Hartnack, Oc. I, Syst. 7).

III. Preparation to show ciliated cells between non-ciliated cells; after Neumann. IV. Vertical section at border of liver to show ciliated epithelium; after Neumann.

A Stoma. B Pigment-cells. C Ciliated cells. D Non-ciliated cells. ]

*b.* *Minute structure* (Fig. 201).

The endothelial cells are attached to each other by cement-substance, easily stained by silver nitrate. The cells covering the general surface of the peritoneal cavity are larger and broader than those covering the mesentery of the small intestine (compare I and II, Fig. 201).

At various points stomata are found, bordered by smaller and more deeply staining epithelium (I, A). The membrane covering the general cavity is also much more pigmented than that covering the mesentery (compare I and II).

Various portions of the peritoneal surface possess ciliated cells, and these cells are usually thicker than the surrounding non-ciliated cells. Such cells are found especially near the openings of the oviducts and on the liver. The dimensions of the cells vary; according to Neumann the average dimensions of ciliated cells on the liver are: 0.006 mm. depth (without the cilia); nucleus, 0.012 mm. long and 0.003 mm. broad. The cells are five- or six-sided and bounded by straight sides (Neumann).]