794 



NERVOUS SYSTEM OF THE HORSE 



part of the thalamus, and (3) the anterior quadrigeminal body (indirectly). The fibers which 

 go to the medial geniculate body appear to belong to Gudden's commissure and to be non-visual 

 in function. The ^dsual fibers, which come from the lateral part of the retina of the same side 

 and the medial part of the retina of the opposite side, terminate about cells in the anterior quad- 

 rigeminal body and the part of the thalamus which corresponds to the pulvinar and lateral genicu- 

 late body of man. From the cells of the former fibers pass to the nuclei of the motor nerves of 

 the eyeball, and complete the reflex arc. Fibers proceed from the cells of the thalamus to the 

 visual area of the cortex in the occipital part of the hemisphere. 



THE OCULOMOTOR NERVE 



The oculomotor nerve (N. oculomotorius) arises by several radicles from the 

 basal surface of the cerebral peduncle, a little lateral to the interpeduncular furrow. 



It turns sharply outward and for- 

 ward, crosses over the cavernous 

 sinus, and continues above the 

 maxillary nerve and in company 

 with the ophthalmic nerve to the 

 foramen orbitale. It emerges 

 through the foramen with the lat- 

 ter nerve and the abducens and 

 divides into two branches. The 

 dorsal branch is short and divides 

 into two twigs which supply the 

 rectus dorsalis and levator pal- 

 pebrae superioris. The ventral 

 branch (Figs. 563, 564) is larger 

 and much longer. It supplies the 

 motor fibers to the ciliary gan- 

 glion (which lies directly on this 

 branch in the horse) and short 

 branches to the rectus medialis 

 and rectus ventralis, and con- 

 tinues forward on the latter to 

 end in the ventral oblique mus- 

 cle. 



The deep origin of the fibers of 

 the oculomotor nerve is in the oculo- 

 motor nucleus, situated in the gray mat- 

 ter of the floor of the cerebral aque- 

 duct in the region of the anterior cor- 

 pora quadrigemina. 



Fig. 645. — Floor of Cranial Cavity of Horse. 

 The roots of the cranial nerves are shown on the left side 

 and are designated by number: /, Anterior cranial fossa; 77, 

 middle cranial fossa; 777, posterior cranial fossa; a, ethmoidal 

 fossa; b, ethmoidal foramen; c, foramen for nasal branch of 

 ophthalmic artery; d, orbital wing of, sphenoid bone; e, optic 

 groove; /, hypophyseal fossa; g, spheno-occipital crest; h, h', con- 

 tour of hypophysis or pituitary body; h", slight elevation repre- 

 senting dorsum sellae; i, k, grooves for nerves and cavernous sinus; 

 /, depression for piriform lobe of cerebrum; m, groove for middle 

 meningeal artery; n, depression for pons; o, foramen lacerum an- 

 terius; p, foramen lacerum posterius; q, incisura carotica; q', inci- 

 sura ovalis; q", incisura spinosa; r, depression for medulla oblongata; 

 s, hypoglossal foramen; i, internal acoustic meatus; u, foramen 

 magnum: r, frontal sinus; w, zygomatic process of temporal bone; 

 X, section of petrous temporal; y, section of occipital bone; z, crista 

 galh; 1, 1', I", dotted lines indicating position of olfactory strise 

 and tract. (After Ellenberger-Baum, Top. Anat. d. Pferdes.) 



THE TROCHLEAR NERVE 



The trochlear nerve (N. tro- 



chlearis)^ is the smallest of the 

 cranial nerves. It arises from 

 the anterior cerebellar peduncle 

 just behind the corpora quadri- 

 gemina, curves outward and for- 

 ward, pierces the tentorium cere- 

 belli, and passes forward along 

 the lateral border of the maxillary 

 nerve (Figs. 635, 636). It emerges from the cranium through a small foramen 

 ' Formerly termed the nervus pathetious. 



