Part 215

The =medulla= is short, wide, and thick. Its ventral face is strongly convex. The pyramids are narrow, short, and close together in front. Near the decussation there is a well defined oval prominence on either side which indicates the position of the posterior olive. The corpus trapezoideum is large; it has no central part between the pyramids. The external arcuate fibers are distinct. The restiform bodies are short and thick and diverge more strongly than in the horse. The floor of the fourth ventricle is only about two-thirds as long as in the horse. The area acustica is a well-marked oval prominence lateral to the middle part of the limiting sulcus. The tuberculum acusticum at the origin of the auditory nerve is very large. The anterior fovea is distinct. The posterior recess of the fourth ventricle communicates through the foramen of Magendie (Apertura mediana) with the subarachnoid space.

FIG. 528.—BRAIN OF COW, DORSAL VIEW.

1, Sulcus transversus; 2, longitudinal fissure; 3, antero-internal frontal gyrus; 4, olfactory bulb; 5, marginal or sagittal pole of hemisphere; 6, lateral fissure (of Sylvius); 7, hemisphere of cerebellum; 8, vermis of same; 9, accessory nerve; 10, dorsal root of first cervical nerve. (Ellenberger-Baum, Anat. d. Haustiere.) ]

The =pons= is smaller, both transversely and longitudinally, than that of the horse. It is strongly convex and has a distinct central depression.

The =cerebellum= is smaller and more angular in form than in the horse. The vermis is large and has a distinct depression on its anterior face for the posterior corpora quadrigemina. The hemispheres are relatively small and are not clearly divided into tabulations. The anterior peduncles are very short.

The =cerebral peduncles= are short. A small eminence in the locus perforatus posticus is caused by the presence of the interpeduncular ganglion. The =internal geniculate body= is prominent. The =pineal body= is long and fusiform, and is often pigmented in spots. The third ventricle forms two considerable recesses in relation to the pineal body: one (R. pinealis) extends up into the body; the other (R. suprapinealis) is a long tubular prolongation in front of it.

The =optic tracts= cross the cerebral peduncles almost at a right angle.

The =pituitary body= is situated in a deep fossa and is surrounded by a plexus of vessels.

The =cerebral hemispheres= are shorter, higher, and relatively wider than in the horse. The frontal poles are small, the occipital large. Viewed from the side, the dorsal surface is strongly convex. The highest point of the dorso-medial border is a little in front of its middle and forms a marked prominence termed the =sagittal= or =marginal pole= (Polus sagittalis s. prominentia marginalis dorsalis). Anterior to this the border drops abruptly, being cut into by the deep transverse fissure. The arachnoid on the basal and anterior parts of the hemispheres is usually pigmented. The =corpus callosum= extends through a little more than a third of the length of the hemisphere. The pattern of the =fissures= and =gyri= of the pallium is somewhat simpler than in the horse.

FIG. 529.—CEREBRAL HEMISPHERES OF OX, DORSAL VIEW.

a, Transverse fissure; b, lateral fissure (of Sylvius); c, coronal fissure; d, diagonal fissure; e, entomarginal fissure; f, marginal fissure; g, ectomarginal fissure; h, suprasylvian fissure. (After Ellenberger, in Leisering’s Atlas.) ]

1. The =lateral fissure= (of Sylvius) is very deep. Its middle branch extends almost vertically upward on the middle of the lateral surface of the hemisphere, and is separated by a gyrus of variable width from the suprasylvian fissure. The anterior branch runs forward about parallel with the sulcus rhinalis anterior, from which it is separated by the short gyri of the insula. The latter are covered to a small extent only by the overhanging gyri (operculum). The posterior branch may run back a distance of only about 1.5 cm. and end in T-shaped manner, or it may join the sulcus rhinalis posterior.

2. The =suprasylvian fissure= is deep and very distinct. It extends in an undulating manner from the lateral surface of the occipital pole to the outer side of the sagittal pole. Here it may be interrupted or may be continued by the =coronal fissure=, which descends to the frontal pole and divides into two short branches.

3. The =diagonal fissure= (S. diagonalis) begins in front of the stem of the lateral fissure and runs upward and forward. Its form is very variable.

4. The =transverse fissure= cuts obliquely into the dorsal border in front of the sagittal pole. It is short and deep and commonly communicates with the suprasylvian and coronal fissures.

5. The =marginal fissure= is distinct. It extends from the sagittal pole to the occipital pole. It is flexuous and deviates outward somewhat in its posterior two-thirds.

6. The =entomarginal fissure= lies medial and parallel to the posterior part of the preceding.

7. The =ectomarginal fissure= is lateral and parallel to the marginal fissure. It does not extend so far in either direction as the latter and is often more or less broken up by annectent gyri.

8. The =sulcus rhinalis= is more open than in the horse, since it is not overlapped by the gyri above it.

9. The =calloso-marginal= fissure is flexuous and not so regular as in the horse. It is often interrupted at or near the level of the genu of the corpus callosum, in which case the =genual fissure= continues it downward.

10. The =crucial fissure= is faint and is confined to the medial surface. It lies about one centimeter in front of the transverse fissure and commonly joins the calloso-marginal fissure below.

11. Short and variable fissures occur in front of and behind the middle branch of the lateral fissure (F. ectosylvia anterior, posterior).

The =olfactory bulb= is much smaller than in the horse. The external olfactory tract is large, the inner one small and not distinct.

The =cranial nerves= have in general the same superficial origin as in the horse. The more important differences in other respects are as follows:

The =oculomotor nerve= is larger than in the horse. It emerges with the fourth, sixth, ophthalmic, and maxillary nerves through the large foramen, which is equivalent to the foramen lacerum orbitale and foramen rotundum of the horse.

The internal branch of the =lacrimal nerve= supplies twigs to the mucous membrane of the frontal sinus; the large outer branch runs backward and supplies the matrix of the horn. The =frontal nerve= emerges from the orbit below the supraorbital process. The =naso-ciliary nerve= is large and sends filaments to the ocular muscles. The =ciliary ganglion= is somewhat larger than in the horse and is connected with the lower division of the oculomotor nerve by several short filaments. In consequence of the absence of the canine and upper incisor teeth the corresponding branch of the infraorbital nerve is naturally wanting. The =mandibular nerve= emerges through the foramen ovale. The =superficial temporal nerve= gives off a large branch which joins the superior buccal division of the facial on the masseter, about half-way between the zygomatic arch and the angle of the jaw. The =otic ganglion= is larger than in the horse. According to Moussu the buccinator nerve furnishes excito-secretory twigs to the parotid and inferior buccal glands.

The =facial nerve= divides into its two terminal branches before reaching the border of the jaw. The =superior buccal nerve= is the larger of the two; it crosses the masseter much lower than in the horse. The relatively small =inferior buccal nerve= runs beneath the parotid or in the gland substance parallel with the border of the lower jaw, crosses under the insertion of the sterno-cephalicus, and runs forward along the depressor labii inferioris. At the point where it crosses the facial vein and parotid duct it gives off an anastomotic branch to the superior nerve. The =auriculo-palpebral nerve= is large.

The =vagus= bears—in addition to the relatively large =jugular ganglion=—a =ganglion nodosum= at the point of origin of the superior laryngeal nerve. The trunk is large. The =pharyngeal branch= is large and anastomoses with the superior and external laryngeal nerves. The latter commonly arises directly from the trunk. The =superior œsophageal trunk= communicates with the splanchnic nerve, contributes twigs to the hepatic plexus, and ramifies chiefly on the right surface of the rumen and the adjacent surface of the abomasum. The =inferior œsophageal trunk= supplies branches to the hepatic plexus and to all the divisions of the stomach.