SECTION I.. The Bones and Joints.

THE BONES AND JOINTS.

THE BONES AND JOINTS.

LITERATURE.

*van Altena*, Commentatio ad quæst. zoologicam in academia Lugduno-Batav. a. MDCCCXXVIII propositam, qua desideratur ut systematice enumerentur species indigenæ reptilium ex ordine batrachiorum addita unius saltem speciei anatomia et præsertim osteographia accurata. Lugd. Bat. 1829. 4^o. With 4 Plates.

*Ange, Martin St.*, Recherches sur les organes transitoires des batraciens. Annales des Sciences naturelles. 1^{re} Série. Vol. XXIV. 1831.

*Bell*, Article Amphibia, in Todd’s Cyclopaedia of Anatomy and Physiology. Vol. I, p. 90. 1835–1836.

*Born, Dr. Gustav*, Ue.d. Nasenholen u.d. Thränennasengang der Amphibien. Leipzig, 1877.

*Bruch, G.*, Beiträge zur Naturgeschichte und Klassification der nackten Amphibien. Würzburger Naturzeitschrift, 1862.

*Bruch, G.*, Neue Beobachtungen zur Naturgeschichte der einheimischen Batrachier. Würzburger Naturzeitschrift, 1863.

*Cuvier*, Recherches sur les ossements fossiles. Vol. V. Pt. II. Paris, 1825.

*Cuvier*, Leçons d’anatomie comparée. Paris, 1835. Vol. I.

*Cuvier*, Ueber die Rückenwirbel der Reptilien und Amphibien, Froriep’s Notizen. Vol. XIII, p. 74. 1826.

*Daudin*, Histoire naturelle des Rainettes, Grenouilles et des Crapauds. Paris, 1802.

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

*Dugès*, Recherches sur l’ostéologie et la myologie des batraciens à leurs différents âges. Paris, 1834. 4^o. With 20 Plates.

*Duméril et Bibron*, Erpétologie générale ou Histoire complète des Reptiles. 1836.

*Gegenbaur*: 1. Ueber Bau und Entwicklung der Wirbelsäule bei Amphibien überhaupt und beim Frosche insbesondere. Abhandlungen der naturforschenden Gesellschaft zu Halle, Vol. VI. Halle, 1861.

2. Untersuchungen zur vergl. Anatomie der Wirbelsäule bei Reptilien und Amphibien. Pt. I. Leipzig, 1862. (Carpus and Tarsus.) With 4 Plates. 4^o.

*Gegenbaur*, Untersuchungen zur vergl. Anatomie der Wirbelthiere. Pt. II. Schultergürtel. 1865.

*Günther*, Ueber geschlechtliche Differenzen in Knochen von lebenden und fossilen Fröschen und Fischen. Annals of Natural History. 1859. Vol. III.

*Hallmann*, Die vergleichende Osteologie des Schläfenbeins, etc. Hannover, 1837. 4^o. With 3 Plates.

*Hoffmann, C. K.*, Beiträge zur Erkenntniss des Beckens der Amphibien und Reptilien. Leyden, 1876.

*Hoffmann, C. K.*, Bronn’s Klassen und Ordnungen des Thierreichs, Vol. VI. Amphibien. Leipzig, 1873–8.

*Huxley*, On the Theory of the Vertebrate Skull; Croonian Lecture, Proc. Royal Society, p. 381. 1858.

*Huxley*, Article Amphibia, Encyclopædia Britannica, IXth Edition. 1875.

*Huxley*, Lectures on the Elements of Comparative Anatomy.

*Huxley*, Handbuch der Anatomie der Wirbelthiere. Deutsche Ausg. von T. Ratzel. 1873.

*Kehrer, G.*, Beiträge zur Kenntniss d. Carpus und Tarsus d. Amphibien, Reptilien, und Säuger. Berichte d. naturf. Gesell. z. Freiburg. 1886.

*v. Klein*, Beiträge zur Anatomie der ungeschwänzten Batrachier. Jahres-Heft. Würtemberg, 1850.

*Köstlin*, Der Bau des knöchernen Kopfs. Stuttgart, 1844. 8^o.

*Leukart*, Zwischenkiefer. Valentins Repertoire. 1841, p. 155.

*Marshall, A. M.*, The Frog. Manchester and London. 2nd Edit., 1885, pp. 45–59.

*Mayer, A. F.*, Beiträge zu einer anatomischen Monographie der Rana pipa. Acad. Caes. Leop. Nov. Acta. 1825. Vol. XII, p. 527; and Isis v. L. Oken. 1825. col. 317.

*Meckel*, System der vergleichenden Anatomie. II. Thl. I. Abthlg. Halle, 1824. 8^o.

*Meckel*, Ueber das Zungenbein der Amphibien. Meckel’s Arch. f. Physik. 1818. Vol. IV, p. 60.

*Mertens*, Anatomiæ batrachiorum prodromus sistens observationes nonnullas in osteologiam batrachiorum nostratium. Halæ, 1820. 8^o.

*Mivart*, On the Classification of the Anurous Batrachians. Proc. Zool. Soc. 1869.

*Morren*, Observations ostéologiques sur l’appareil costal des batraciens. Bulletins de l’Acad. de Bruxelles, 1835, II.--Mémoires de l’Académie, 1837. Tome X.

*Müller*, Beitrag zur Anat. d. Amph. Zeitschrift f. wissenschaftliche Zoologie. Vol. IX. 1858, p. 178.

*Parker, W. K.*, Structure and Development of the skull of the common frog. Phil. Trans. 1871, p. 137.

*Parker, W. K.*, Skull of Batrachia. Phil. Trans. 1876, p. 601.

*Parker, W. K.*, and *Bettany, G. T.*, Morphology of the Skull. London, 1877.

*Pouchet*, Note sur les différences que le sexe imprime au squelette des grenouilles. Comptes rendus. Vol. XXV, p. 761. 1847.

*Reichert, K. B.*, Vergleichende Entwicklungsgeschichte des Kopfs der nackten Amphibien nebst den Bildungsgesetzen des Wirbelthierkopfs im Allgemeinen und seinen hauptsächlichen Variationen durch die einzelne Wirbelthier-Classe. Königsberg, 1838.

*Remak*, Untersuchungen über die Entwicklung der Wirbelthiere. Berlin, 1855.

*Rösel, von Rosenhof*, Historia naturalis ranarum nostratium. Nörnberg, 1758.

*Rudolphi and Breyer*, Observationes anatomicae circa fabricam Ranae pipae. Berolini, 1811.

*Rusconi*, Développement de la grenouille commune. Milan, 1826.

*Rusconi*, Sulle metamorfosi delle osse della testa della rana. Annali di Bologna. 1^{re} Série, Vol. II, p. 357.

*Schneider*, Historia amphibiorum. Jenae, 1799.

*Shaw*, General Zoology. London. Vol. II, Pt. I, p. 167.

*Stannius*, Zootomie der Amphibien (Handb. der Zootomie der Wirbelthiere, 2. Buch). 2nd Edit. Berlin, 1856. 8^o.

*Stricker*, Untersuchungen über die Entwicklung des Kopfes der Batrachier. Arch. f. Anat. u. Physiol. 1864, pp. 52–76.

*Stricker*, Beiträge zur Biologie der Batrachier. Verhandl. der Wiener Akademie. 1866. Vol. XVI, pp. 451–456.

*Townson, R.*, Facts and Observations in Natural History. London, 1799.

*Troya*, Mémoire sur la structure singulière du tibia et du cubitus des grenouilles et des crapauds. Mémoires de mathématique et de physique présentées à l’acad. de Paris. Vol. IX. 1780.

*Wagner*, Icones Zootomicae. Leipzig, 1841.

*Wagner*, Lehrbuch der vergleichenden Anatomie. Leipzig, 1834–1835.

*Wiedersheim, R.*, Lehrbuch d. vergleichenden Anatomie der Wirbelthiere auf Grundlage d. Entwickelungsgeschichte. Jena, 1886. 2nd Edit.

*Wiedersheim, R.*, Elements of Comparative Anatomy of Vertebrates, translated by W. Newton Parker. London, 1886.

THE BONES AND JOINTS.

The consideration of the differences in form, number, and histological structure, which the parts of the skeleton present during the various stages of development does not fall within the scope of this book: we have here but to deal with the adult frog.

The skeleton is made up of histologically different materials; these are:--(1) bone, (2) hyaline cartilage, and (3) so-called calcified cartilage. Concerning the last it is necessary to make some observations. I have chosen for it the name calcified cartilage in place of the more usual names ‘cartilaginous bone’ or ‘primordial ossification,’ as by this term its nature appears to be expressed without any ambiguity: it is hyaline cartilage in which calcareous particles have been deposited to a greater or less extent: in the fresh state it has the appearance of moderately firm cartilage; when dry it becomes opaque and white, like the calcareous crusts on the cartilages of the Plagiostomata. The calcareous material is deposited in the cartilage in finer or coarser granules; after removal of the lime by means of acids, the cartilaginous structure becomes apparent although not so perfectly as in unchanged cartilage.

This calcified cartilage is widely distributed in the frog’s skeleton: very many parts, which in higher animals consist only temporarily of this substance during the transition from cartilage to bone, are in the frog formed of it throughout life. It is especially well-marked in the epiphyses of the long bones in the hand and foot, in the bones of the shoulder-girdle, etc. To avoid repetition later on I will briefly describe it as found in the first-mentioned situation. Dugès has described its external appearance, while Bruch has made us acquainted with its histological peculiarities. If a long bone of the frog be dried, the femur for example, the middle part is found to differ considerably from the epiphyses in colour and in other particulars. The shaft alone has the appearance of bone, the epiphysis consisting of a white, opaque, firm substance, resembling plaster of Paris or lime, but which in the fresh moist state is exactly like cartilage. The epiphyses, which are fitted to the ends of the diaphysis like the cap of a stick-handle, have sharply defined margins (Fig. 3), as is well seen in Figs. 36, 39, 45, and 46. If a section be made through the epiphysis and part of the diaphysis, the long tube of true bone is seen to cease abruptly above o, Fig. 3, and over the end of it the epiphysis E is fixed. This epiphysis consists almost entirely of calcified cartilage c′, and has merely a superficial layer of hyaline cartilage A. The bony cylinder of the diaphysis o, which contains the marrow M in its interior, is shut off from the epiphysis by hyaline cartilage, the cells of which are arranged in transverse layers, o.

Longitudinal section through the upper extremity of the femur of Rana esculenta, magnified.

A Hyaline cartilage (articular cartilage). c Hyaline cartilage closing end of bony cylinder. c′ Calcified cartilage of epiphysis. D Bony cylinder of diaphysis. E Epiphysis. M Marrow cavity. o End of diaphysis. ]

I. THE VERTEBRAL COLUMN.

The vertebral column of the frog consists of ten bones, viz. nine true vertebrae, and the rod-shaped urostyle, which alone is almost as long as all the remaining vertebrae.

I. GENERAL DESCRIPTION OF THE NINE VERTEBRAE.

*a.* The bodies of the vertebrae are compressed from above downwards; the posterior surface of each body, with the exception of the eighth, presents an articular head covered with cartilage; the anterior surfaces, with the exception of the ninth, present corresponding articular depressions, covered with cartilage.

*b.* The arches, which have somewhat sharp margins both before and behind, bear the following processes:-- *1.* The *articular processes* (Figs. 4 and 5 o o) are similarly placed to those of the dorsal vertebrae of man: they project horizontally, the cartilaginous articular surfaces on the posterior processes being directed downwards, those on the anterior upwards.

Vertebrae of Rana esculenta, seen from below, twice the natural size.

1 to 9 First to ninth vertebræ. c Urostyle. o o Articular processes. sc The two facets for articulation with the urostyle. ]

*2.* The *transverse processes* (Figs. 4 and 5 t t′) are strong, flat, and of very varying size and direction. The transverse processes of the fourth vertebra are the longest, those of the third only a little shorter; the shortest are those of the seventh and eighth. The atlas has no transverse processes. Those of the second and third vertebrae project directly outwards and slightly downwards; those of the fourth, fifth, and sixth upwards and backwards. The seventh and eighth project more directly outwards and at the same time backwards; the ninth upwards and markedly backwards. All the transverse processes have cartilaginous epiphyses; the largest are those of the second, third, fourth, and ninth vertebrae.

*3.* The *spinous processes* are generally small, but individually of varying size, appearance, and direction. The longest are those of the third, fourth, and fifth vertebrae; these are, in transverse section, of a three-sided prismatic form, as in the dorsal vertebrae of man; they are directed backwards and provided with cartilaginous epiphyses. The spinous processes of the sixth and seventh are shorter, compressed from side to side, project directly upwards, and are usually without cartilaginous epiphyses; that of the eighth is still shorter. As regards the spinous processes, those of the third, fourth, and fifth vertebrae resemble those of the dorsal vertebrae in man; those of the sixth, seventh, and eighth, lumbar vertebrae. The ninth has either no spinous process or only a rudimentary one. The first and second vertebrae may be looked upon as cervical vertebrae: the second has a short spinous process with a cartilaginous epiphysis. In the first, the cartilage which unites the two halves of the arch represents the rudiment of a spinous process.

Vertebral column of Rana esculenta, from above, twice nat. size.

1 to 9 First to ninth vertebræ. c Urostyle. o o Articular processes. sc Facets for articulation with the urostyle. t t′ Transverse processes. ]

II. DESCRIPTION OF PARTICULAR VERTEBRAE.

*1.* The *atlas* or *first vertebra* has a thin body, compressed from above downwards, and an arch. The body has posteriorly a slightly raised, cartilaginous, articular head, which is broader transversely: in front it has two oval articular facets, which are separated from each other by a median projection. Each facet is concave, and directed forwards, outwards, and slightly upwards. The arch is completed above by cartilage, which projects slightly to form the rudiment of a spinous process. The hinder margin of the arch bears two articular processes. Transverse processes are wanting.

*2.* The *second vertebra* presents all the general characters of an ordinary vertebra, except that the transverse processes are directed somewhat downwards.

*3.* The transverse processes of the *third vertebra* are longer than those of the second: each is directed downwards, is broader at its extremity than at its base, and bears a hammer-shaped cartilaginous epiphysis larger than those of the remaining transverse processes.

*4.* The transverse processes of the *fourth vertebra* are the longest: each is broader at its free end than at its base, is directed upwards and backwards, and provided with a cartilaginous epiphysis.

*5*, *6*, *7*. The transverse processes of the *fifth*, *sixth*, and *seventh vertebrae* are smaller, contracted towards their free extremities, and directed upwards.

*8.* The *eighth vertebra* is distinguished from the rest by its body possessing no articular head. It presents, at each end, a concave articular depression. The transverse processes resemble those of the seventh.

*9.* The *ninth vertebra* unites the vertebral column with the hip-bones, and is hence to be regarded as a *sacrum*. The body bears on its anterior surface an articular head for articulation with the eighth vertebra: on its posterior surface are two small rounded and closely approximated processes (Figs. 4 and 5 sc) for articulation with the urostyle. The transverse processes are strong, broader at the free ends than at their origin, directed upwards and backwards, and provided with cartilaginous epiphyses.

III. ARTICULATIONS OF THE VERTEBRAE.

The articular heads and depressions of the vertebral bodies, together with the joint surfaces of the articular processes, are covered with hyaline cartilage. The periosteum of the bodies, as also that of the articular processes, forms true capsular joint ligaments. The articulations of the vertebrae are still further strengthened by longitudinal fibres, which extend along the anterior and posterior surfaces of the vertebrae, and correspond to the ligamentum vertebrale commune anticum et posticum of man. Between the vertebral arches are membranes which represent the ligamenta intercruralia. Between the spinous processes are bands of connective tissue which form ligamenta interspinalia. (For the articulation of the atlas with the occiput, see page 24.)

IV. STRUCTURE OF THE VERTEBRAE (Figs. 6 and 7).

Transverse section through a vertebra of Rana esculenta, magnified.

c Cancellous bone. Ch Chorda dorsalis. Ch′ Sheath of chorda dorsalis. o Compact bone on the upper and lower surfaces of the body. ]

Each vertebral body consists of a cylinder of compact bone, which is directly continued into the bony substance of the arch. In the interior of the cylinder is found an isolated persistent vestige of the chorda dorsalis (Ch): this is surrounded by cancellous bone (c), which extends backwards towards the articular head and forwards directly into the articular cartilage, compact bone being absent in these parts. In a transverse section of a vertebral body the following parts are seen (Fig. 6):--*a.* An outer layer of compact bone (o) (the transverse section of the above-mentioned cylinder), which is formed of parallel lamellae of varying thickness. These, according to Gegenbaur, and as I can confirm, are arranged in well-defined groups, each of five to eight lamellae. The number of the secondary lamellae increases with the age of the animal. *b.* In the interior, in the form of a cylinder, is the remnant of the chorda dorsalis. It consists of a double sheath (Ch′) and contents (Ch) composed of chorda-cells. *c.* Immediately around the persistent portion of the chorda lies the central part of the vertebral body, formed by transformation of the vertebral cartilage and of the bases of the original cartilaginous arches. At each side of the chorda are large marrow-spaces (c), filled with cells, from which proceed narrower canals, winding in various directions, and anastomosing freely with one another both before and behind. Their walls are constituted partly of true bone, partly of cartilage.

Longitudinal section through the posterior half of the body of a vertebra of Rana esculenta.

a Cartilage of the head. c Cancellous bone. o Shell of compact bone. ]

V. THE UROSTYLE (Figs. 8 and 9).

The *urostyle* is a long, median, rod-like bone, which projects backwards, midway between the two hip-bones, and terminates over the anus. The anterior end (Fig. 8 a) is the thicker and broader part of the bone, and has two articular depressions (Fig. 9) for articulation with the two facets of the ninth vertebra. The hinder end is pointed and cylindrical, and terminates in a cartilage, which is fixed in the tubular end of the bone. The middle portion is almost cylindrical, and has a groove along the ventral surface which gradually becomes less marked behind. The dorsal surface bears a ridge (Figs. 8 and 9 s), which is high and thick in front, becomes sharper and less prominent as it proceeds backwards, and gradually disappears towards the hinder third of the bone, so that in transverse section the anterior two-thirds of the bone appear triangular, with a ventral and two lateral surfaces: while the hinder third is cylindrical. The anterior portion of the bone contains a canal, canalis vertebralis (Fig. 9 c.v.), which is a continuation of the vertebral canal, along which the hindermost spinal nerves pass. On each side of the anterior portion of the urostyle are small apertures (Fig. 8 c.c.), which lead into canals (canales coccygei), which open into the vertebral canal, and through which the coccygeal nerves pass. In front of these openings and partly overhanging them are small triangular projections (Fig. 8) (processus transversarii): these, however, are not constant, and are more often found in R. esculenta than in R. temporaria, in which latter species the openings are smaller.

Urostyle of Rana esculenta, seen from the side, twice nat. size.

c Ventral border. c.v. Canal. vertebralis. s Dorsal ridge (pr. spinos.). ]

Urostyle of Rana esculenta, seen from the side, twice nat. size. A bristle is passed through the canal. vert. and out through the canal. coccyg. of the right side.

a Anterior extremity. c.c. Canal. coccyg. s Dorsal ridge (pr. spinos.). ]

II. THE SKULL.

The flat form of the frog’s head, as in batrachians generally, depends upon the wide separation of the jaw-bones of the two sides, and on the large size of the orbital cavities and the horizontal direction of their floors. The outer circumference of the head forms a parabolic frame (Figs. 10 and 11), composed of the maxillary (m), premaxillary (i), and quadratojugal bones (j). In the middle of this curved framework lies the elongated prismatic cranium. Anteriorly, this is attached to the fore-part of the frame by means of the cartilaginous skeleton of the organs of smell (Fig. 11 e′); posteriorly, it widens out into two transverse arms (p), which contain the organs of hearing. From this base, on either side, a bony strut, composed of the posterior arms of the squamosal (t′) and of the pterygoid bones, passes backwards to the hinder end of the frame. The anterior arm of the squamosal bone (t) does not quite reach the framework, but is attached to it by ligament alone. Between the last-named arm posteriorly, the cranium on the inner side, and the maxillary frame-work laterally, is a large space representing the orbital and temporal fossae of human anatomy.

Skull of Rana esculenta, seen from above, twice natural size.

e Sphenethmoid. fn Nasal. f.p. Fronto-parietal. i Premaxillary. j Quadrato-jugal. m Maxillary. o Exoccipital. op Opisthotic. p Prootic. pt Pterygoid. pt′ Posterior limb of pterygoid. t Squamosal. t′ Posterior arm of the same. ]

Skull of Rana esculenta, seen from below, twice natural size.

c Cartilaginous wall of skull. e Sphenethmoid. e′ Cartilaginous skeleton of nose. h′ Stylo-hyoid. i Premaxillary. m Maxillary. m′ Quadrate tract. o Exoccipital. p Prootic. p′ Anterior arm of prootic (ala magna autt.). p″ Trigeminal foramen. pl Palatine. pt Pterygoid. pt′ Posterior arm of pterygoid. s Parasphenoid. v Vomer. ]

A. THE CRANIUM.

The cranium of the frog is a prismatic tube, wide behind, narrow in front, and formed in great part of cartilage (Figs. 15 and 17). Our indigenous species are characteristically distinguished from one another by peculiarities in the form of the cranium. In R. esculenta it is long and narrow, in R. temporaria short and wide. The superior surface in the former is markedly concave, while in the latter it is flat, and in R. oxyrhinus arched. These differences are readily recognised in the living animal.

*The Bones of the Cranium.*

*1.* The *exoccipital bones*, ossa occipitalia lateralia, Cuvier (Figs. 10, 11, 12, 14, 16 o).

*Cuvier*, l. c., p. 387, Pl. XXIV, bb.--*Dugès*, l. c., n. 14.--*Parker* and *Bettany*, l. c., p. 166, exoccipitals.

Skull of Rana esculenta, seen from behind, twice natural size.

a Stapes. a′ Columella auris. a″ Extrastapedial. c Condyles of exoccipitals. h Stylo-hyoid. o Exoccipitals. p Prootic. p′ Process to which the jaw is attached. t Squamosal. ]

These paired bones form the hinder part of the cranium; they bound the foramen magnum, and articulate with the vertebral column. They are imbedded in the cartilaginous matrix of the skull, and are separated above by an unossified part of this matrix (occipitale superius, Dugès), which represents the tabular portion of human anatomy: below they are separated by a similar part (occipitale basilare, Dugès) which represents the body of the occipital bone. They therefore properly represent only the condylar portions (partes condyloideae) of the human occipital bone. Each possesses a cartilaginous articular head, for articulation with the first vertebra: these converge below, and surround the lower half of the circumference of the foramen magnum. This latter has, in R. esculenta, a transversely oval outline; in R. temporaria, a somewhat heart-shaped outline, with the apex directed upwards: in accordance with this the whole bone is wider than high in the first species; and in the latter it is higher than it is wide. From the upper and outer border of the foramen magnum on each side a ridge runs obliquely outwards and downwards, in which lies the suture between this bone and the prootic bones. This bony ridge (processus mastoideus, autt.) is usually cartilaginous in R. esculenta, even in old animals; in R. temporaria, even in young specimens, it is bony. In the latter species the bones unite very early, while in the former they remain separated by the primitive cartilage. Between this crest and the processus condyloideus there is a depression (fossa condyloidea), with a hole (foramen condyloideum) through which the vagus nerve leaves the cranium. The exoccipital take part in the formation of the labyrinth of the ear, as will be noticed later on.

Articulation of the Exoccipital Bones with the Atlas. From the middle of the anterior surface of the body of the atlas a ligament arises, representing to a certain extent the lig. suspensorium dentis, and attached to the basal portions of the exoccipital bones.

*2.* The *prootic bones*, ossa petrosa, Cuvier (Figs. 10, 11, and 12 p).

*Cuvier*, rocher, l. c., p. 388, Pl. XXIV, ee.--*Dugès*, n. 12, rupéo-ptéréal.--*Stannius*, ala temporalis.--*Meckel*, Schädelstück des Schläfenbeins.--*Parker* and *Bettany*, l. c., prootic.

These paired bones lie at the sides and in front of the exoccipital bones. As already explained, they remain in R. esculenta separated from these by cartilage, while in R. temporaria they early enter into bony union with them; this is due to the complete ossification of the processus mastoideus in the latter species, as stated above. The prootics form the lateral expansions of the posterior part of the skull in which the organs of hearing are placed. The large cavity which contains the ear labyrinth is completed by the exoccipital: internally it opens freely into the skull, and externally on the posterior wall of the skull through the foramen ovale, which is formed by both these bones. The postero-lateral part of the prootic usually remains cartilaginous: at the side and in front of the foramen ovale this cartilage is pierced by a small opening, through which passes the nervus facialis or ramus tympanicus n. vagi (Volkmann). At the side there is a process to which the suspensorium of the lower jaw is attached (Fig. 12 p): behind this is a hollow in which the auditory ossicles lie, and which may be designated fossa tympanica (Fig. 12 t). The anterior border of the bone forms the hinder and inner walls of the orbit. Here also is the trigeminal foramen (Fig. 11 p″) through which the N. trigeminus and the several nerves for the muscles of the eye pass; it represents the foramen ovale, for. rotundum, and the fissura orbitalis superior (sphenoidal fissure) of the human sphenoid bone. The foramen is sometimes, especially in young animals, only a notch, which is completed by cartilage. On account of the relation of this part (Fig. 11 p′) of the bone to the nerves which pierce it, the whole bone has been named by Stannius the ala magna or temporalis of the sphenoid; it has been also looked upon as a bone which contains these elements, as by Dugès, who on this account calls it rupéo-ptéréal.

Skull of Rana esculenta, seen from below, twice natural size.

c Cartilaginous wall of skull. e Sphenethmoid. e′ Cartilaginous nasal skeleton. h′ Stylo-hyoid. i Premaxillary. m Maxillary. m′ Quadrate tract. o Exoccipital. p Prootic. p′ Anterior arm of prootic. p″ Trigeminal foramen. pl Palatine. pt Anterior arm of pterygoid. pt′ Posterior arm of pterygoid. s Parasphenoid. v Vomer. ]

Appendages of the Prootic Bones.

1. The *styloid cartilage*. From the cartilaginous portion of the prootic the styloid cartilage runs downwards, backwards, and inwards, and is continued directly into the anterior cornu of the hyoid bone (Figs. 11 h′ and 12 h).

2. The *auditory ossicles*.

a. A thick cartilaginous disc, the operculum (Fig. 12 a), closes the foramen ovale.

b. To the operculum is attached a bony, club-shaped piece, the columella auris (Fig. 12 a′), which has at its inner, thicker end a cartilaginous epiphysis, the *interstapedial*; it lies transversely with the apex directed outwards, and this longer portion is the *mediostapedial*.

c. To the apex of the mediostapedial is attached, at an obtuse angle, the third cartilaginous piece, the *extrastapedial* (Fig. 12 a″). It is attached to the tympanic membrane, and by its upper portion is fastened to the cartilaginous tympanic ring by a smaller piece, the *suprastapedial*.

3. The *tympanic ring* (annulus tympanicus) is an annular cartilaginous frame; or more exactly, has the shape of a short, truncated cone, as it narrows towards the middle line: it is attached to the squamosal bone. (See Organ of hearing.)

*3.* The *parasphenoid*, os sphenoideum, Cuvier (Figs. 11 and 16 s).

*Cuvier*, l. c., p. 388, Pl. XXIV, d.--*Dugès*, n. 8.--*Meckel*, Theil des Grundbeins.--*Parker* and *Bettany*, l. c., parasphenoid.

A large portion of the base of the cranium is taken up by this cruciform bone. Of the two longitudinal median processes, the posterior is by far the shorter, and lies in front of and partly below the cartilaginous os occipitale basilare. The anterior longer longitudinal arm closes in the greater part of the cranium from below, and articulates by its outer edges with that part of the prootic bones often described as the alae magnae, and also with the cartilage lying in front, which forms the greater part of the lateral walls of the cranium. The anterior extremity of the bone articulates with the palatine bones. The transverse arms lie on the under surface of the exoccipitals and of the prootics.

The greater width of the cranium in R. temporaria is associated with the greater relative width of the anterior arm of this bone.

4. The *fronto-parietal bones*, ossa fronto-parietalia, Cuvier (Figs. 10 and 14 fp).

*Cuvier*, l. c., p. 387, Pl. XXIV, c. c.--*Dugès*, n. 1.--*Parker* and *Bettany*, l. c., fronto-parietal.

These are a pair of somewhat long, flat bones, which form the principal part of the upper wall or roof of the cranium, and cover in superiorly the cartilaginous cranium, which is here, in great part, persistent. They are united in the middle line by the sagittal suture; posteriorly they articulate with the exoccipital and prootic bones; anteriorly with the sphenethmoid, which they overlap like tiles. The outer margin of each bone is bent somewhat downwards (Fig. 16 fp), and between it and the parasphenoid there is a space in the wall of the cranium which is closed in by cartilage and connective tissue only.

These bones are narrower in R. esculenta, and along the sagittal suture are depressed into a groove: where the superior surface bends down to become lateral the edges are much more prominent. In R. temporaria the bones are broader and flat or even somewhat arched. The latter condition is still more marked in R. oxyrhinus.

*5.* The *sphenethmoid*, os ethmoideum (Figs. 10, 11, 14, and 16 e).

*Cuvier*, os en ceinture, l. c., p. 387, Pl. XXIV, a.--*Dugès*, n. 15.--*Rathke*, anterior or sphenoidal wing (Vortr. z. vergl. Anat. d. Wirbelthiere, Leipzig, 1862, p. 42).--*Meckel*, Riechbein, l. c., p. 502.--*Parker* and *Bettany*, l. c., ethmoid.

The long tubular cranium is completed anteriorly by a single bone, which forms at once the roof, floor, and lateral walls. It is consequently more or less ring-shaped, on which account it has been named ‘os en ceinture’ by Cuvier. Only the posterior portion is annular, however: the anterior portion forms a double canal, with a median partition, for the passage of the nerves of smell, and as these canals are widened out anteriorly, this part of the bone helps to complete the nasal cavities, which, however, are bounded for the most part by cartilage, as described below. In some species of frogs (as for example R. occellata, Rathke) this cartilage is partly ossified.

The sphenethmoid has on each side a small bony canal, running forwards and inwards, through which the ramus nasalis of the first division of the trigeminal nerve passes.

The *cartilaginous skeleton of the nose* (Figs. 14 and 16 n, n″, n‴, n⁗). The anterior borders of the funnel-shaped cavities of the sphenethmoid pass into cartilage, which forms two capsules, separated from each other by a median cartilaginous septum, and opening laterally. We can distinguish, (a) a cartilaginous septum, forming a continuation of the bony one; (b) the floor of the nasal cavity, narrower behind, wider in front; (c) a roof somewhat narrower than the floor. The floor and roof are united in front by an arched surface. From this cartilaginous capsule various processes project, which unite it to other portions of the facial skeleton: firstly, from the most posterior portion of the capsule there passes transversely outwards a bar of cartilage (sn), which, widening, becomes continuous with the cartilage (sp″) forming the basis of the anterior arm of the pterygoid bone. From the anterior angle a cartilaginous process passes outwards (Figs. 14, 16 n″), which is attached to a projection on the anterior end of the maxillary bone; from the same spot a horn-shaped cartilaginous process (n″, n‴) curves round backwards and towards the middle line. This projection bounds the nasal cavity externally, sending off a free process (n‴) on the way, and ends with a double point on the roof of the cartilaginous nasal cavity (n⁗). On the floor of the nasal capsule, on either side, is a knob-shaped cartilaginous eminence, running from behind, forwards and outwards; this may be regarded as an indication of a turbinated bone. From the anterior wall there passes into each nasal cavity an almost horizontal, partly ossified plate (c.n.), ending posteriorly in a free pointed border. These are the cornets of Dugès (l. c., p. 12, Pl. I, Figs. 1, 5), who correctly regarded them as turbinated bones. Cuvier described them as rudimentary nasal bones.

Cartilaginous basis of the skull of Rana esculenta, from above, twice natural size. Cartilage shown by stippling.

a.n. Wings of nasal cartilage. c.n. Concha narium. e Sphenethmoid. ff′ Foramina of cranium. fn Nasal. fp Fronto-parietal. i Premaxillary. j Quadrato-jugal. m Maxillary. n, sn Cartilaginous nasal skeleton. n′, n″, n‴ Processes of the cartilage. o Exoccipital bones. p. Prootic. pt Anterior arm of pterygoid. pt′ Posterior arm of pterygoid. s′ Cartilaginous cranium. sp Cartilage of suspensorium. sp′ Cartilage under the squamosal. sp″ Cartilage under the pterygoid. t^1 Anterior } t^2 Middle } arm of the squamosal. t^3 Posterior } ]

The alar cartilages of the nose have still to be described. They are (a.n.) shell-shaped cartilages, hollowed out on the inner sides and decreasing in width from before backwards. They are movably attached by their anterior broader ends to the tips of the projecting portions of the premaxillary bones, and are so arranged as to bound the lateral margins of the nasal apertures, which they overlap.

Nasal cartilages of frog, front view.

an Concha narium. i Premaxillary bones. i′ Ascending process of same. m Upper jaw. m′ Lower jaw. n Olfactory capsule. ]

*6.* The *cartilaginous basis of the skull*, Primordial cranium (Figs. 14, 16).

*a.* If the fronto-parietals be removed, (Figs. 14, 16), a cartilage (s′) is found which partially closes the cranial cavity, and which is usually perforated on either side by a foramen (f′). More anteriorly in the median line is found a space (f) which extends to the sphenethmoid bone, and is only closed by connective tissue: posteriorly the cartilage extends between the exoccipitals as far as the foramen magnum, representing the os occipitale superius.

*b.* The base of the cranium is (Fig. 16) also partly cartilaginous. If the parasphenoid (s) be removed we find above it a cartilage (s′) which passes backwards between the exoccipitals, and extends as far back as the foramen magnum: it corresponds to the os occipitale basilare.

Cartilaginous skull of Rana esculenta, from below, twice natural size. Cartilage shown by stippling.

c Cartilage of prootic. e Sphenethmoid. fp Fronto-parietal. i Premaxillary. j Quadrato-jugal. m Maxillary. n, sn Cartilaginous nasal skeleton. n′, n″, n‴, n⁗ Processes of nasal cartilage. o Exoccipital. p Prootic. pl Palatine. pt Pterygoid. pt′ Articular surface for pterygoid. r Optic foramen. r′ Foramen for N. abducens. s Parasphenoid. s′ Cartilaginous cranium. sp Cartilage of suspensorium. sp′ Cartilage under squamosal. sp″ Cartilage under pterygoid. v Vomer. ]

*c.* The sides of the cranium are formed almost entirely of cartilage. This cartilage fills the space bounded by the nasals above, the parasphenoid below, the so-called ala magna of the prootic bone behind, and the sphenethmoid in front; and has in its posterior part an aperture (r) through which passes the nervus opticus, and below this a smaller one (r′) for the nervus abducens. The extent of the cartilage in the antero-posterior direction is greater in R. esculenta than in R. temporaria, or in other words the sphenethmoid stretches further back in the latter than in the former.

B. THE BONES OF THE FACE.

Cartilaginous basis of the skull of Rana esculenta, from above, twice natural size. Cartilage shown by stippling.

a.n. Wings of nasal cartilage. c.n. Concha narium. e Sphenethmoid. ff′ Foramina of cranium. fn Nasal. fp Fronto-parietal. i Premaxillary. j Quadrato-jugal. m Maxillary. n, sn Cartilaginous nasal skeleton. n′, n″, n‴ Processes of the cartilage. o Exoccipital bones. p. Prootic. pt Anterior arm of pterygoid. pt′ Posterior arm of pterygoid. s′ Cartilaginous cranium. sp Cartilage of suspensorium. sp′ Cartilage under the squamosal. sp″ Cartilage under the pterygoid. t^1 Anterior } t^2 Middle } arm of the squamosal. t^3 Posterior} ]

The *Suspensorium*.

7. The *squamosal bones*, ossa tympanica, Cuvier (Figs. 10, 14 t).

*Cuvier*, oss. foss., V, 2. 390, Pl. XXIV, Figs. 1, 2 n.--*Dugès*, temporo-mastoidien, n. 10.--*Meckel*, Articular part of temporal.--*Hallmann* and others, quadrate-bone.--*Parker* and *Bettany*, l. c., squamosal.

The suspensorium, which forms the articulation between the cranium and the lower jaw, is T shaped; and consists of cartilage covered by bone. Of the three arms of the T the anterior has a free pointed extremity (Fig. 14 t^1) at the postero-lateral margin of the temporo-orbital fossa: it forms a true processus zygomaticus, and is bound to the upper jaw by ligaments. In R. temporaria it is comparatively much shorter than in R. esculenta. The posterior upper arm (t^2) articulates with the prootic bone: the third or lower arm (t^3), supported by a cartilage, runs backwards and downwards to unite with the side of the broad hinder extremity of the quadrato-jugal bone.

The cartilaginous basis of the suspensorium (Fig. 17 sp, sp′) is a direct continuation of the cartilaginous basis of the cranium, and proceeds from it to the outer extremity of the prootic; from this point the cartilage runs backwards and divides into two branches; of these, one (sp′) retains the original course backwards and outwards towards the articulation of the lower jaw, and in conjunction with the quadrato-jugal (j) forms this joint. The other (sp″) is directed forwards along the anterior arm of the pterygoid bone; it widens in front (sn), and becomes directly continuous with the cartilaginous strut described above as projecting from the hinder part of the cartilaginous olfactory capsule.

*8.* The *quadrato-jugal bones*, ossa jugalia, Cuvier (Figs. 10, 17, 19 j).

*Dugès*, tympano-malléal, n. 11.--*Cuvier*, l. c., p. 399, Pl. XXIV, Figs. 1 2 o.--*Hallmann*, quadrato-jugal bone, l. c., p. 39.--*Parker* and *Bettany*, l. c., quadrato-jugal.

This is a small process of bone, likened by Dugès to a comma, which rests by its posterior broader extremity on the cartilage of the mandibular arch, and forms with it a portion of the articular head for the lower jaw. The anterior extremity is pointed, directed forwards, and attached by ligament to the maxillary bone.

*9.* The *pterygoid bones*, ossa pterygoidea (Figs. 10, 11, 17, 19 pt).

*Cuvier*, l. c., p. 389, Pl. XXIV, Figs. 1, 2 m m.--*Dugès*, n. 9.--*Parker* and *Bettany*, l. c., pterygoid bones.

These bones, shaped like the Greek letter λ, possess each three arms: of these the middle one is attached to the under surface of the prootic bone by a cartilaginous process (Fig. 18 sp); the hinder grooved arm lies upon the under surface of the cartilaginous suspensorial arch (Fig. 18 sp′); and the anterior arm (pt) runs forwards along the inner border of the anterior ramus of the suspensorium (sp″), in contact with the maxillary, palatine, and nasal bones.

The cartilage just mentioned, by means of which the middle arm of the pterygoid is connected with the cranium (compare Fig. 18), proceeds from the cranial origin of the cartilaginous arch (sp), turns downwards and then forms a sort of articular head (cpt), which is articulated to an oval flat elevation of the prootic cartilage by a movable joint. Externally the articular head curves somewhat abruptly into the bony substance (Fig. 18 pt) of the pterygoid bone.

Origin of the suspensory cartilage (sp) from the skull, with attachment of the pterygoid; front view. Cartilage shown by stippling.

cpt Cartilaginous epiphyses of the pterygoid bone, from the cartilaginous suspensorium. j Quadrato-jugal bone. pt Pterygoid bone. sp Origin of suspensorial cartilage from the skull. sp′ Hinder arm of same. sp″ Anterior arm of same. ]

Cartilaginous skull of Rana esculenta, from below, twice natural size. Cartilage shown by stippling.

c Cartilage of prootic. e Sphenethmoid. fp Fronto-parietal. i Premaxillary. j Quadrato-jugal. m Maxillary. n, sn Cartilaginous nasal skeleton. n′, n″, n‴, n⁗ Processes of nasal cartilage. o Exoccipital. p Prootic. pl Palatine. pt Pterygoid. pt′ Articular surface for pterygoid. r Optic foramen. r′ Foramen for N. abducens. s Parasphenoid. s′ Cartilaginous cranium. sp Cartilage of suspensorium. sp′ Cartilage under squamosal. sp″ Cartilage under pterygoid. v Vomer. ]

*10.* The *maxillary bones*, ossa maxillaria superiora, Cuvier (Figs. 10, 11, 17, 19 m).

*Cuvier*, l. c., p. 389, Pl. XXIV, Figs. 1, 2 k k.--*Dugès*, n. 4, maxillo-jugal.--*Parker* and *Bettany*, l. c., maxillary bones.

These are elongated, curved bones, narrower behind, broader in front, and forming with the quadrato-jugals the bony support of the face. The superior surface is convex and directed outwards, the inferior surface is grooved and bears teeth along the outer edge of this groove. From the upper and inner border of the anterior half of this bone a process (processus frontalis) passes upwards, which articulates with the nasal bone. The anterior extremity of the bone articulates with the premaxillary bone, the posterior with the quadrato-jugal.

The maxillary bone articulates at its anterior end (Fig. 19 n″) with a process of the cartilaginous capsule of the nose. The broad plate of cartilage (Fig. 19 n), under cover of the processus frontalis, connects the hindermost transverse portion of the nasal cartilage with the cartilage which runs forwards from the suspensorium upon the anterior arm of the pterygoid.

*11.* The *nasal bones*, ossa fronto-nasalia, Dugès (Figs. 10, 17 fn).

*Cuvier*, frontale anterius, l. c., h.--*Dugès*, n. 2.--*Meckel*, nasal bone.--*Parker* and *Bettany*, l. c., nasal bones.

These flat, triangular bones, which rest upon the nasal cartilages (n), assist to bound the orbital cavities in front, and are connected by their external angles with the maxillary bone on either side.

*12.* The *premaxillary bones*, ossa intermaxillaria (Figs. 10, 11, 17, 19 i).

*Cuvier*, l. c., p. 388, Pl. XXIV, Figs. 1, 2 f f.--*Dugès*, n. 3.--*Parker* and *Bettany*, l. c., premaxillary bones.

These two bones are united in the middle line: each consists of a tooth-supporting portion, which completes the maxillary arch, and an ascending process, to the apex of which the nasal cartilage is articulated by a movable joint (an). As muscles are attached to this process, it becomes a lever, by which movements are effected.

Skull of Rana esculenta, seen from below, twice natural size.

c Cartilaginous wall of skull. e Sphenethmoid. e′ Cartilaginous nasal skeleton. h′ Stylo-hyoid. i Premaxillary. m Maxillary. m′ Quadrate tract. o Exoccipital. p Prootic. p′ Anterior arm of prootic. p″ Trigeminal foramen. pl Palatine. pt Anterior arm of pterygoid. pt′ Posterior arm of pterygoid. s Parasphenoid. v Vomer. ]

*13.* The *palatine bones*, ossa palatina (Figs. 19, 20 pl).

*Cuvier*, l. c., p. 389, Pl. XXIV, Figs. 1, 2 i i.--*Dugès*, n. 7.--*Parker* and *Bettany*, l. c., palatine bones.

Are two transverse bony bars, situated under the anterior portion of the sphenethmoid bone on either side: each extends outwards from the apex of the parasphenoid to the maxillary bone, where this gives off its ascending process to the nasal bone.

*14.* The *vomers*, vomer (Figs. 19, 20 v).

*Cuvier*, l.c., p. 389, Pl. XXIV, Figs. 1, 2 l l.--*Dugès*, n. 6.--*Parker* and *Bettany*, l.c., vomer.

A pair of flat bones, placed horizontally on the under surface of the cartilaginous nasal capsule in the triangular space between the palatine bone and the anterior portion of the arch of the jaw. They limit the outer border of the floor of this capsule, which lies in a groove on the dorsal surface of the bone. The outer border of each bone has three processes, and between them two notches; the hinder of these notches bounding the posterior nares. The inner borders of the two bones touch, and the under surface of each bears a transverse row of small, pointed teeth.

*15.* The *mandible*, maxilla inferior (Fig. 21).

*Cuvier*, l.c., p. 398, Pl. XXIV, Figs. 1, 2 rst.--*Dugès*, n. 16, 17, 18, 19.--*Parker* and *Bettany*, l.c., mandibular arch.

A Mandible of Rana esculenta, from above, nat. size. B External view of left side, } twice nat. size. C Angulosplenial, } 1. Angulosplenial. 2. Dentary. 3. Mentomeckelian. 4, 4′ Meckel’s cartilage. a. Rudimentary processus coronoideus. b. Groove for Meckel’s cartilage. ]

The mandible consists of two bony arches united by ligament in the middle line, and each formed of four pieces. These are, (1) the *angulosplenial*, a strong, bony piece (Fig. 21 C, B1, A1), which forms the inferior and internal part of the lower jaw; below, it extends posteriorly, as far as the articulation; in front, it is attached to the dentary. In the greater part of its length it has a groove directed upwards and outwards (C, b), and above has a process which represents the processus coronoideus: (2) the *dentary* (A 2, B 2), a bony lamella which rests on the outer surface of the anterior half of the angulosplenial, and articulates in front with *Meckel’s cartilage*; it is a thin, flat lamella of bone; (3) in the groove of the angulosplenial is found a cartilage occupying its entire length (A 4, B 4), *Meckel’s cartilage*; it is broader behind, and here forms the articular fossa of the lower jaw; anteriorly it is covered by the dentary, and articulates with the (4) *mentomeckelian* (A 3, B 3) at its anterior end, which is bound to its fellow of the opposite side by ligaments, and unites the two halves of the lower jaw.

The upper part of Meckel’s cartilage, which forms the joint with the suspensorium, must be regarded as the articulare; to this also belongs the anterior, ossified portion of the mentomeckelian; the dentary, which covers Meckel’s cartilage, must represent the os dentale; the first and largest bone, the angulosplenial, which lies on the inner side of the cartilage, must be considered as the os operculo-angulare, Dugès, for it contains the elements of these bones.

Hyoid of Rana esculenta, twice nat. size.

H Body; h h′ processes. H′ Anterior horn. H″ Posterior horn. ]

*16.* The *hyoid bone*, os hyoideum (Fig. 22).

*Parker* and *Bettany*, l.c., hyoid.

This consists of a broad, thin, cartilaginous plate, with processes passing from it as represented in the figure. We distinguish in it:--(*a*) the body (H), somewhat oblong, and wider in front than behind. From the anterior angles there projects on either side a blunt rounded process (h); from either posterior angle a more pointed process (h′). (*b*) The anterior cornua (H′) (cornua styloidea) project from the anterior border of the body, first in a forward direction, then in a curve backwards and upwards (compare Fig. 12), to unite with the cartilage of the prootic bone. Where the direction of these cornua is changed each sends off a short blunt process. (*c*) The posterior cornua (cornua thyroidea) (H″) are bony rods which run from the hinder margin of the body, diverge posteriorly, and enclose the larynx.

III. THE STERNUM (Fig. 24 es, hs).

*Cuvier*, l. c., p. 401, Pl. XXIV, Fig. 31 e f.--*Dugès*, n. 27, 28.--*Parker* and *Bettany*, l. c., sternum.

The bones of the sternum are in very close relationship with the shoulder-girdle, and some difference of opinion exists as to the relations of the several parts.

Omosternum of Rana esculenta, twice nat. size.

a Anterior, p Posterior extremity. ]

The following parts must be regarded as undoubtedly belonging to the sternum:--

*1.* An anterior part, consisting of a bony and a cartilaginous portion.

a. The *omosternum* (Figs. 23, 24 e.s.) is a bony rod, wider behind, narrower in front, and supports

b. The *episternum* (Fig. 24 es′), a semicircular plate of calcified cartilage, with a thin free border of unchanged hyaline cartilage.

*2.* A posterior part, which also consists of a bony and a cartilaginous portion.

Shoulder-girdle and sternum of Rana esculenta, twice nat. size. The scapula and suprascapula are turned outwards.

c. Connecting cartilage. cl. Clavicles and precoracoids. co Coracoid. es. Omosternum. es′ Episternum. h Hyaline cartilage. hs. Sternum proper. hs′ Xiphisternum. o Bone. o′ Calcified cartilage. sc. Scapula. sc′ Suprascapula. ]

a. The *sternum proper* (Fig. 24 h.s.), a rod of cartilage ensheathed in bone, broader in front and narrower behind. To its posterior extremity is attached

b. The cartilaginous *xiphisternum* (Fig. 24 hs′), a plate, the shape of which is best understood by referring to Fig. 24, and the structure of which is similar to that of the episternum.

*3.* The *epicoracoids* lie between the episternum and the sternum proper: they are a pair of narrow cartilages, closely applied to each other and placed between the ventral ends of the precoracoids and coracoids, see p. 40.

IV. THE BONES OF THE ANTERIOR EXTREMITY.

A. BONES OF THE SHOULDER-GIRDLE.

The shoulder-girdle of the frog (Fig. 25) consists of four bones, two in the upper or *scapular portion*, and two in the lower or *coracoid portion*.

*1.* The *scapular portion*.

*a.* The *suprascapula*, pars suprascapularis scapulae, scapula superior s. omolita (Figs. 25 s′, 26, 27). This forms the upper, thinner portion. It is trapezoid in shape, its narrowest, thickest, and lowest border articulating with the scapula. The remaining three borders are free; the posterior and superior borders are very considerably thinned out, the inferior surface is curved towards the ventral surface. Only the thin upper and hinder borders (hh) are of hyaline cartilage; the middle portion (co) consists of calcified cartilage; the lateral part (o) and the anterior border (o′) of true bone.

Shoulder-girdle of the frog in transverse section, diagrammatic.

c Connecting cartilage. c′ Epicoracoids. cl Clavicles. h Humerus. s Scapula. s′ Suprascapula. ss Articulation of these two. v Vertebra. ]

The bony part forms a thin plate striated both radially and concentrically with the margin. The anterior border (o′) is bent on itself so as to form a groove (Fig. 27). The dorsal surface of this bony plate is quite smooth, and covered only by periosteum; the ventral surface, on the contrary, is for the most part covered by an even layer of calcified cartilage (Fig. 27 co′). This passes directly into the second portion of calcified cartilage (co); so that if the whole be dried, the thin hard lamina of bone can easily be split away from the underlying parchment-like cartilage. The layer of calcified cartilage is, however, not so complete that the suprascapula can be said to consist of calcified cartilage.

Suprascapula of Rana esculenta, from above, twice nat. size.

co Calcified cartilage. h Hyaline cartilage. o Bony portion. o′ Anterior curved border. ]

Suprascapula of Rana esculenta, from below, twice nat. size.

co Calcified cartilage. co′ Layer of calcified cartilage on the under surface of the bone. h Hyaline cartilage. o Bony portion. o′ Anterior curved border. ]

Left scapula of Rana esculenta, from below, twice nat. size.

a Anterior border. c.a. Cavitas articularis. l Outer border. m Inner border. p Posterior border. ]

Scapula seen from behind, twice nat. size.

c.a. Cav. articularis. d Dorsal process. v Ventral process. ]

*b.* The *scapula* (Figs. 25 s, 28, 29) is a long, flat, four-cornered plate of compact bone, contracted in the middle, and wider at either end. From above (Fig. 28 l) it descends to the shoulder-joint with a slight curvature, with the convexity directed outwards. The inferior or ventral border (Fig. 28 m), which assists in the formation of the shoulder-joint, is cleft into two processes, a ventral and a dorsal. This may be best seen by looking at the border of the bone from behind or before (as in Fig. 29). The lower ventral process (Fig. 29 v) may be regarded as the acromion, or at least as a rudiment of the acromion, i. e., spina scapulae. The upper dorsal process evidently represents a rudimentary processus coracoideus. The anterior border (Fig. 28 a) is free, somewhat sharp, and slightly concave; the posterior (Fig. 28 p), also concave, is free externally; while internally, where the division of the ventral border commences, it takes part in the formation of the articular cavity of the shoulder (Figs. 28 and 29 c.a.).

Articulation with the suprascapula. The scapula consists of a shell of compact bony tissue and an inner portion of cancellous tissue; this latter passes, at the boundary between this bone and the suprascapula, through an intermediate layer of calcified cartilage, which is directly continuous with the cartilage of the suprascapula. The compact superficial layer ceases where the calcified cartilage begins, and the periosteum of the scapula passes directly into the perichondrium of the suprascapula.

*2.* The *ventral portion* of the shoulder-girdle consists of three parts, which lie one behind the other.

*a.* The larger and posterior bone, the *coracoid* (Figs. 24 co, 30), is contracted in the middle, and expanded at either end, especially at the sternal end. The inner half is flattened from above downwards; externally it becomes more cylindrical. The anterior and posterior borders are markedly concave; the outer border (Fig. 30 l) articulates by means of a cartilage with the proc. coracoideus of the scapula; the inner border (m) is separated from its fellow of the opposite side by the epicoracoids. This inner border is so broad, that it almost touches the inner end of the clavicle (Fig. 24 cl.). A *coracoid foramen* is thus formed between the two bones, similar to the foramen ovale of the pelvis.

Left coracoid, twice nat. size.

a From below. b From behind. l Outer extremity. m Inner extremity. ]

Clavicle of the left side, twice nat. size.

l Outer extremity. m Inner extremity. ]

*b.* The small anterior bones of the ventral portion of the shoulder-girdle (Figs. 24 cl., 31), I, like Cuvier and others, regard as *clavicles*. Dugès (n. 33) names them ‘acromial.’ Each bone is narrower than the coracoid, smaller internally (m), broader externally (l), and articulates by this broader end with the cartilage uniting the dorsal and ventral portions; the inner extremity rests upon the epicoracoid. The clavicle is grooved on its superior and posterior surfaces in almost its whole length; the groove widens externally (l), and contains

*c.* The *precoracoid* (Fig. 34 cl′), a slender bar of cartilage, connecting the anterior edge of the scapula with the sternum.

Right shoulder-girdle of Rana esculenta, from above.

ca Cav. articularis. c c Cartilage. cl Clavicle. co Coracoid. sc Scapula. sc′ Suprascapula. ]

Hinder border of the scapula and coracoid, with the connecting cartilage and shoulder-joint, twice nat. size.

c Connecting cartilage. d Dorsal process. co Coracoid. sc Scapula. v Ventral process. ]

Clavicular cartilage of a young specimen of Rana esculenta, enlarged to the adult size.

c Connecting cartilage. e Epicoracoids. c′ Ligament between the two cartilages. cl Clavicle. cl′ Clavicle and precoracoid. co Coracoid. co′ Cartilage of same. es Omosternum. hs Sternum proper. ]

*Cartilages* of the shoulder-girdle (Figs. 24, 32, 34). A cartilage (c), described by Dugès as the ‘paraglénal,’ connects the scapula with the coracoid, and converts the notch between the two processes (s and v) on the inner border of the scapula into an aperture opening posteriorly into the glenoid cavity, and which is filled up by the lining cartilage. This cartilage connects the two processes with the coracoid; being thicker between this and the proc. coracoideus, it takes an important share in the formation of the floor of the glenoid cavity. At the outer extremity of the clavicle the cartilage projects and is then continued in the groove on this bone towards the middle line (Figs. 32, 34), where it widens out, and is united by its external margin with the sternum, thus forming the precoracoid as already described, see p. 40. These connections are best seen in young animals, as is shown in Fig. 34.

The clavicle (cl) is of ossifying cartilage; the cartilage (c), the epicoracoid, is very large, and hyaline, and at cl runs directly into the epicoracoids, which are here united mesially by ligament. In the fully developed animal the whole of the epicoracoid changes to calcified cartilage, as also does the precoracoid lying in the groove of the clavicle.

B. BONES OF THE FORE LIMB.

*1.* The *arm* has but one bone.

Fig. 35. Fig. 36. Fig. 37.

Humerus of Rana Humerus of Rana, Humerus of Rana esculenta, female, esculenta male, esculenta, female, seen from below. seen from below. outer side.

Figures twice natural size.

c Anterior extremity. c′ Posterior extremity. cd Crista deltoidea. cm Crista medialis. t trochlea.]

The *humerus*, os humeri (Figs. 35, 36, 37). The shaft of the humerus is, on the whole, cylindrical, the middle part being the narrowest; its dorsal surface is slightly concave, the ventral surface convex. In the upper half the cylindrical form is indistinct, from the presence of a well-marked crest (crista deltoidea) upon the under or ventral surface. The hinder half of the bone has very different shapes in the two sexes: in the female it remains cylindrical as far as the elbow-joint; in the male, on the posterior surface, where the crista deltoidea ceases, a marked ridge (crista medialis) arises, which gradually winds inwards and terminates at the inner condyle. This sexual difference is found in all the three species described in the Introduction, and it would seem that this ridge increases in height during the pairing season. The muscle which arises from this process is the flexor carpi radialis (Fig. 74 Fc), and it attains, in the males, a very large size at the same period; indeed, it is at its origin twice as broad as in the female. Dugès has incorrectly stated that this crista is a peculiarity of Rana temporaria, and is wanting in Rana esculenta. Pouchet first observed that it was a sexual distinction.

The anterior articular extremity presents a rounded head, which is somewhat flattened externally. The inferior ventral border is sharp, and developed into the above-mentioned bony crest (crista deltoidea); the free border is arched and curved outwards. Above, on the outer surface of the head, is found an eminence which may be a rudimentary tuberc. maius. The inner half of the head is articular.

The posterior articular extremity consists of a rounded head (c′), attached to the posterior extremity of the shaft; internal to this is a small trochlea (t), placed upon the inner condyle. The external condyle is but small. The head is embraced by these condyles. Upon the under surface, above the head, is the fossa cubitalis anterior. The structure of the two articular extremities of the humerus differs; the upper, as in long bones generally (see page 16), consists of hyaline cartilage surrounded by calcified cartilage, which again is covered by hyaline articular cartilage; the lower extremity is composed of spongy bone, with roundish marrow spaces, and for the most part covered by a layer of calcified cartilage.

The *shoulder-joint*. The socket is formed by the posterior border of the scapula, by both the processes of that bone, the outer portion of the coracoid, and besides these by cartilage, which forms the articular surface already described (Fig. 33). In the macerated bone the floor of the socket opens dorsally into a fossa between the processes of the scapula (Fig. 32). This opening, in the natural condition, is closed by synovial membrane only; the cartilage covering the rest of the space being absent (the sac may easily be inflated, either from the joint itself or through the opening). The margin of the socket consists of a labrum, partly fibrous and partly cartilaginous, which is easily removed entire. The capsule, which is attached beneath the caput humeri, arises from this. From the articular cartilage of the ventral margin of the socket, and from the adjacent part of the scapula, proceeds a strong band, which is inserted into the flattened outer surface of the head.

*2.* The *forearm*.

Radio-ulnar of the right side of Rana esculenta, twice nat. size.

r Radius. r′ Capitulum radii. u Ulna. u′ Olecranon. ]

The *radio-ulnar*, os antibrachii (Fig. 38). The two bony elements of the forearm are fused into one, which, however, shows traces of its compound character. Of these two bones, that which forms the inferior (in man anterior) border is the radius, the other the ulna. The relative positions of the bony elements are such that they appear to be in a state of semi-pronation; by this the thumb-border of the arm is directed downwards (in man forwards). The two bones so united form a flattened, tube-like bone, the grooved surfaces of which are directed inwards and outwards respectively; the borders being dorsal and ventral. The shaft of the bone is narrower above, becoming gradually wider below. In the upper half, the groove showing the line of junction of the two bony elements is scarcely visible, and it appears as though this part consisted of ulna alone, the radius not reaching so far; below the groove is more marked. The upper articular extremity appears to consist of an olecranon (Fig. 38 u′) and a processus coronoideus (r′), between which is the greater sigmoid cavity (cavitas sigmoidea major) for the processus cubitalis humeri. A more careful examination shows this to be incorrect: the portion of the concave articular surface, which lies in the immediate neighbourhood of the ventral border, undoubtedly represents the articular surface of the capitulum radii, and the upper portion of the articular surface (at u′) belongs to the ulna and articulates with the trochlea (Figs. 35, 36 t) of the humerus. The inner border of the upper extremity of the bone articulates with the groove t of the humerus. The inferior extremity forms one of the usual cartilaginous epiphyses, enclosing the two bones. That part of the extremity corresponding with the radius is triangular and convex, it is prolonged upon the inner or under surface of the bone by means of a process; the ulnar portion of the bone forms a capitulum. The structure of the inferior extremity is that of epiphyses in general, except that there are two medullary cavities in a common sheath of calcified cartilage; the anterior head consists of cancellous tissue, with a covering of calcified cartilage.

*3.* Bones of the *hand* (Fig. 39).

*Dugès*, Pl. VIII, Figs. 37, 38, 39, 40, 41, 42, 43, 52.

*a.* Bones of the *wrist*, ossa carpi. These are arranged in two rows, proximal and distal. The proximal or anterior row has three bones, viz.:--

1. Os lunatum, the middle bone (Fig. 39 l), Dugès, n. 38, articulates with the radial part of the articular surface of the radio-ulnar by a concave surface; with the large bone of the second row (hc) it articulates by means of a rounded head; and with the two other bones of this row, os naviculare (n) and pyramidale (p), with the former by a saddle-shaped surface, with the latter chiefly by ligament. The bone is irregularly cuboid; the dorsal and palmar surfaces are non-articular. With Dugès I regard this bone as os lunatum; Mertens regards it as os naviculare.

Bones of the forearm and hand of Rana esculenta, right side, dorsum, twice nat. size.

a Os antibrachii. hc Os capitato-hamatum. l Os lunatum. m Ossa metacarpi. n Os naviculare. p Os pyramidale. r Radial portion of the radio-ulnar. t Os multangulum majus or trapezium. t′ Os multangulum minus or trapezoides. u Ulnar portion of the radio-ulnar. I-V First to fifth fingers, the fifth only of os metacarpi, the second and third of two, fourth and fifth of three phalanges. ]

2. Os pyramidale (Fig. 39 p), Dugès, n. 37, articulates with the ulnar part of the posterior articular extremity of the radio-ulnar. Anteriorly the bone has a facet which receives the capitulum ulnae, and alongside this a small flat surface which articulates with the radius. Posteriorly, opposite to the second row, it presents a long raised articular surface, extending from the dorsum to the palmar surface; and on the palmar aspect of the bone is a ridge running from before backwards. Mertens names this bone os lunatum.

3. Os naviculare (Fig. 39 n), Dugès, n. 39. The third bone of the first row does not articulate with the bones of the forearm. It is connected with the os lunatum by a saddle-shaped surface, posteriorly with the os capitatum by means of a concave surface. On the inner surface is a small concave articular facet for the os multangulum minus or trapezoides (Fig. 39 t′). The convex palmar surface of the bone articulates with the os multangulum majus (t); the radial side is non-articular, and with the os lunatum forms a ridge directed forwards. Mertens names this bone os triquetrum. It is evident, however, that if the arrangement in man obtains as a standard, the nomenclature of Dugès, which I have here used, is correct; but the os naviculare is no longer in contact with the articular surface of the os antibrachii.

The second or distal row also consists of three bones:--

4. Os capitato-hamatum (Fig. 39 hc), Dugès, n. 40, 41, 42, corresponds with the os capitatum and hamatum, which are here fused together. It is the largest bone, and articulates with all three bones of the first row; it is crescentic, with the concavity directed posteriorly, and on the convex surface has three facets for the three outer ossa metacarpi.

5. Os multangulum minus, s. trapezoides (Fig. 39 t′), Dugès, n. 43, is a small bone lying next to the foregoing; it articulates with the os metacarpi II, and anteriorly with the os naviculare. Dugès considers it to be the os trapezium.

6. Os multangulum majus, s. trapezium (Fig. 39 t), is a small bone, which is placed on the convex palmar auricular side of the os naviculare. Dugès regards this bone as os metacarpi pollicis (Dugès, n. 44), Mertens as multangulum minus. It appears to me that the interpretation here given is justified, because it articulates with the rudiment of the thumb, and as it possesses no resemblance to a long bone it cannot be regarded as an os metacarpi.

*Structure of the carpal bones.* All the carpal bones consist of calcified cartilage, though variations due to age occur in the amount of the deposit.

*Wrist joint.* As stated above, the os lunatum and os pyramidale are articulated with the forearm. In addition to the capsules uniting the parts, there are strengthening ligaments, two of which require special mention. One of these arises from the palmar surface of the posterior extremity of the ulna, and passes to the sharp palmar ridge of the os pyramidale, where it is attached, and is inserted into the os capitato-hamatum; the second ligament passes in a similar manner on the palmar surface from the radius to the os naviculare. Between the two ligaments there is on the volar surface a deep excavation.

Bones of the forearm and hand of Rana esculenta, right side, dorsum, twice nat. size.

a Radio-ulnar. hc Os capitato-hamatum. l Os lunatum. m Ossa metacarpi. n Os naviculare. p Os pyramidale. r Radial portion of the radio-ulnar. t Os multangulum majus or trapezium. t′ Os multangulum minus or trapezoides. u Ulnar portion of the radio-ulnar. I-V First to fifth fingers, the first only of a metacarpal, the second and third of two, fourth and fifth of three phalanges. ]

*Movements* of the hand. The two bones of the forearm being firmly united, pronation and supination, as in man, are impossible. The normal position, as already remarked (see radio-ulnar), is that of semi-pronation (compare Figs. 2 and 74). If the animal be in its natural posture, with the arm bent at the elbow (Fig. 1) it can touch the ground with the ulnar border only; but when the whole surface of the hand rests upon the ground, the action is brought about as follows: the plane of the carpus is in extension parallel with that of the forearm; in flexion, almost at right-angles with that plane (Fig. 74) The os lunatum glides on the prolongation of the articular surface on the inner palmar surface of the radius, while the os pyramidale is held firmly by the ligament just described. The hand follows the movement of the os lunatum, and at the same time the three outer ossa metacarpi gliding with it inwards, the fingers of the hand turn inwards.

*b.* The Bones of the *metacarpus*, ossa metacarpi (Fig. 40 m). Of these there are five: the *second* to the *fifth* are of about equal length; the first, forming the rudiment of the thumb, hidden beneath the skin, is much shorter. This metacarpal bone of the *thumb* is regarded by Dugès and others as the first phalanx. My reason for describing it as a metacarpal has already been given. This bone also presents differences in the two sexes. Meckel’s observation that it exists only in the male is incorrect; it is a large, broad and sickle-shaped mass of calcified cartilage or even true bone, while in the female it is simply a small cartilaginous rod; as this almost entirely disappears in dried specimens, Meckel’s statement is explained. The *second* finger has in the frog assumed the functions of the thumb, and, in the males, in the breeding season swells and undergoes an essential alteration of structure. The metacarpal of this finger also displays differences in the sexes, being in the male stronger, broader, and on the inner side provided with a spine-like prolongation, for the tendon of the abductor digiti II (pollicis) longus, which attains an unusual development during the breeding season. The remaining metacarpal bones, the *third*, *fourth*, and *fifth*, are of similar form, the last being provided with a tubercle. The anterior articular extremities are rather broad and concave, and the posterior have rounded heads.

*c.* The *phalanges*, phalanges digitorum. The hand has four fingers and the rudiment of a fifth, which latter is completely hidden under the skin, and as already explained, consists of a metacarpal only. Of the four fingers, the fourth is the longest, the third the shortest, the second and fifth of intermediate and about equal length; the fourth and fifth fingers have each three phalanges, the second and third have each two. Their shape is not unlike that of the human phalanges.

V. THE BONES OF THE HINDER EXTREMITY.

A. BONES OF THE PELVIC GIRDLE (Fig. 41).

The *pelvis* has a characteristic V-shape, the pubic and ischiatic bones of the two sides together forming a vertical plate (a p), which divides anteriorly into the two iliac bones (il). The pubic and ischiatic bones being united by their median surfaces, one can only speak of the pelvic cavity as the space between the two ilia.

*1.* The *ilia*, ossa ilii (Fig. 42 il). In these a broader part or body can be distinguished, which takes part in the formation of the acetabulum (a). The hinder and broadest part of the bone is joined to the corresponding portion of its fellow by ligament; anteriorly the two diverge, bounding a cone-shaped cavity, the pelvis. The suture, by which the body of the iliac bone is united with the ischiatic and pubic bones, runs from above downwards through the middle of the acetabulum (Fig. 42, from p through the acetabulum to is). Inferiorly and in front the united ilia form a prominence (s), which represents the symphysis oss. pub. of man. The expanded portions of the ilium rest directly over the articular cavity by means of a somewhat constricted part or root. The ala is a sabre-like bone, with the sharper, more convex border directed upwards; the more concave, thicker border downwards. The two surfaces, of which the inner is grooved, are directed respectively inwards and outwards. The broader part of the blade springs directly from the neck or root (at il′), and at this end of the sharp convex border is a process, process. sup., from which the tendon of the m. vastus externus arises. The anterior end of the blade is a hollow cylinder, containing cartilage, movably articulated to the transverse process of the last vertebra or sacrum.

Pelvis of Rana esculenta, from below, nat. size.

a Acetabulum. il Iliac bone. p Pubic bone. ]

Pelvis of Rana esculenta, left side, twice nat. size.

a Acetabulum. d Upper sharp border. il Iliac bone. il′ Superior process. is Ischium. is′ Tuber ischii. p Os pubis. s Inferior process of the ilium. v Lower border of same. ]

*2.* The *ischia*, ossa ischii (is), are irregular, four-cornered plates of bone, united together by the whole extent of their inner surfaces. The vertical plate formed by the union of the two bones takes only a very small share in the formation of the articular cavity. Above, it has a somewhat sharp border, continued with the ilium into a process (is′) corresponding with the united tubera ischii; the hinder border, which is united below with the pubic cartilage, is curved.

Horizontal section through the iliac, pubic, and ischiatic bones.

a Acetabulum. il Ilium. is Ischium. p Pubic cartilage. s Ligaments which unite the bones of opposite sides. ]

*3.* The *pubes*, os pubis (Figs. 41, 42, 43 p). Ossified pubic bones do not exist; even in old animals they are composed of calcified cartilage. Each is a triangular cartilage, wedged between the ilium and ischium, but also taking part in the formation of the acetabulum. The pubes of opposite sides are, as shown in section in Fig. 43, united by ligaments in the median plane.

B. BONES OF THE HIND-LIMB.

*1.* The *thigh*.

The *femur*, os femoris (Fig. 44). The shaft is cylindrical, with a slight double or S-shaped curve. In the anterior portion the convexity is directed upwards, in the two hinder thirds downwards. Towards the hinder extremity it is flattened from above downwards. The anterior extremity is a rounded articular head placed directly on the shaft like that of the humerus. This head is somewhat flattened from side to side; and in structure resembles that of the humerus. The inferior extremity is rounded below, but flattened above (towards the hollow of the knee) and behind.

*Hip-joint.* The articular cavity is deepened by a fibrous ring, labrum cartilagineum, which fits closely upon the caput femoris; from this labrum the joint-capsule arises, to be inserted behind the head; close to the lower border of the cavity a ligamentum teres arises, which is inserted into the caput femoris.

*2.* The *leg*.

Femur of Rana esculenta, right side, twice nat. size.

a Anterior extremity. p Posterior extremity. ]

*Tibio-fibula*, os cruris (Fig. 45). This consists of a single bone, the os cruris; it is often called the tibia, but presents, however, distinct indications of being formed of two bones, the tibia and fibula. The shaft is not quite straight; it is thinner in the middle and flattened from above downwards. On the upper as also on the lower surface of the bone is a groove, passing from the middle towards each extremity; this deepens as it proceeds, and is an indication of the compound nature of the bone. In the middle of each surface of the bone is the opening of a canal, through which a bristle may be passed: the canal has bony walls. The medullary cavity is, for the most part, double, being single only in the middle. The anterior extremity is articular, and presents a median groove, which is prolonged on to the under surface. The posterior extremity forms a transverse condyle, which has at its inner part a notch for the tendon of the m. tibialis posticus.

Tibio-fibula of Rana esculenta, twice nat. size, seen from below.

a a Grooves. f Foramen nutritium. t Anterior articular extremity. t′ Posterior articular extremity. t″ Groove on malleolus internus for tendon of m. tibialis posticus. ]

The *knee-joint* consists of a capsule strengthened by the insertions of numerous tendons. Within this the articular surfaces of the femur and tibio-fibula are connected by means of fibro-elastic bands, which spring from the latter bone and cross each other, thus representing the lig. cruciata. The articular surfaces are moreover deepened by loose semilunar cartilages, corresponding with the inter-articular cartilages of the knee-joint of man. In addition, on either side of the joint, are found auxiliary ligaments.

Section of the tibio-fibula through the under extremity.

a Cartilaginous epiphysis. m Marrow cavities. t″ Connecting mass. t t′ The two cylinders of bone. ]

*3.* The *foot* (Fig. 47).

*a.* The *ankle*, ossa tarsi. The *tarsus* consists of two rows of bones.

α. The *proximal row* consists of two long tubular bones (Fig. 47 ac), which are parallel to each other, and undoubtedly correspond with the *astragalus* (talus) and *calcaneum*. The bones are separated in the middle, but approach each other at either end. The outer of these bones (c) I have named calcaneum, following Cuvier and Dugès; the inner, astragalus (a). The two bones are surrounded and enclosed at their anterior and posterior extremities in a common epiphysis of calcified cartilage, which has the usual structure found elsewhere. The ligamentum calcanei, which will be described below (see Muscles of Foot, Fig. 88 lc), may be regarded as an unattached process of the heel.

β. The *distal* row of the tarsals are all composed of calcified cartilage. They are:--

1. Os cuboideum (Fig. 47 cb), a flat plate of cartilage, concave in front, convex behind, placed between the common epiphysis of the astragalus and calcaneum (ac) and the ossa metatarsi II and III. This corresponds, as Dugès suggests, with the separated os cuboideum and cuneiforme III of other batrachians, e. g. Bufo.

2. On the inner side of the above, between the astragalus and metatarsus I lies a small body, concave in front, convex behind, which we may regard, with Dugès, as the analogue of the os naviculare (Fig. 47 n).

Right foot of Rana esculenta, palmar surface, twice nat. size.

a Astragalus. ac Common epiphysis. c Calcaneum. cb Os cuboideum. h First, h′ second cartilage of supplemental toe. m Ossa metacarpi. n Os naviculare. I to V First to fifth toe. ]

3. This latter supports a cartilage which forms a projection on the inner border, covered with skin. This consists of closely-united pieces, a small round, basal piece (h), and a flattened beak-like piece (h′). Dugès considers these pieces as the first and second ossa cuneiformia; I rather incline to Meckel’s opinion that they represent a rudimentary hallux, the first being the os metatarsi, the second a phalanx. Both are composed of calcified cartilage; in R. temporaria the lime-deposit seems to be less than in R. oxyrhinus and R. esculenta, and the projection consequently softer.

*b.* The *metatarsal bones*, ossa metatarsi (Fig. 47, m I-V). The five ossa metatarsi are long, thin tubular bones, the anterior articular extremities of which are broader above and narrow below, hence are wedge-shaped, and anteriorly present flat surfaces for articulation with the tarsus. The shafts are long and thin; the posterior extremities have rounded heads. The comparative length of these is as follows: the fourth is the longest, then come the third, fifth, second, and first in order. In structure they resemble other tubular bones.

*c.* The *phalanges*, phalanges digitorum (Fig. 47). The total lengths of the separate toes correspond with that of the ossa metatarsi, but the distinctive differences are increased, partly by the difference in number and partly by the varying lengths of the phalanges. The first and second toes have each only two phalanges, the third and fifth have each three, the fourth, which is the longest, has four. The terminal phalanges are somewhat hooked towards the plantar surface.