THE CRANIAL NERVES. 507 



Gegenbaur (Lankester), A, 515-522, and Balfour, A, II, 374-383, 

 and in the papers there cited. See also A. M. Marshall {4). 



§ 1379. In the following brief descriptions of the cranial nerves, 

 only the ectal or superficial or apparent origins are given. Their 

 ental (real or deep) origins in man are presented briefly in Gray and 

 Quain, and more fully in Meynert (Strieker, A, 727-751), and in 

 special papers. 



§ 1380. (I) Nervi olfactorii, N. oL, the olfactory nerves.— Fig. 110 ; § 1160. Gray, 

 A, 620 ; Quain, A, I, 526. 



The true olfactory nerves of the cat and man are soft fibrous fasciculi which pass from 

 the surface of the pero through the olfactory foramina of the cribriform plate of the eth- 

 moid bone (Fig. 60, 88), to be distributed to the nasal mucosa (§ 1398, membrana Schnei- 

 deriana). 



On account of the small size of the Lobus olfactorius in man, it was formerly regarded 

 as a nerve, and is still often so called. As shown both by development and by comparison 

 with the lower animals, it is really a protrusion or lobe of the brain. 



§ 1881. (II) Nervus opticus, N. op., the optic nerve.— Fig. 110, 116, 117; PI. I, 

 Fig. 3 ; PI. II, Fig. 3, 4 ; PL III, Fig. 5 ; PI. IV, Fig. 16, 18, 19. Gray, A, 628 ; Quain, 

 A, I, 527. 



Each optic nerve is a cylindrical white cord springing from the side of the chiasma 

 (§ 1202) and passing through the optic foramen (Fig. 57, Fm. op.) to the eyeball. 



The optic nerves are formed by protrusions of the jirimitive diencephalon, and are 

 hence, like the olfactory lobes, regarded by Gegenbaur (Lankester), A, 515, as prolonga- 

 tions of the brain. 



The cavity is obliterated, and in man the fibers constituting the nerve have been 

 traced not only to the thalami and geniculata, but also to the optici. We have not traced 

 them carefully in the cat. 



§ 1383. (Ill) Nervus oculomotorius, i\r. ocm., the oculomotor nerve. — Fig. 116 ; PI. 

 II, Fig. 3. Gray, A, 640 ; Quain, A, I, 528. 



The trunk of this nerve is cylindrical and about 1 mm. in diameter. It arises, slightly 

 flattened, from the Area intercruralis, about 2 mm. from the meson and just caudad of the 

 cimbia (§ 1303), is closely associated with the ophthalmic division of the N. trigeminus, 

 and emerges therewith by the Fm. lacerum anterius to be distributed to all the muscles 

 of the eyeball which are not supplied by the trochlearis and abducens ; it goes also to the 

 levator palpebrae dorsal is muscle. 



§ 1383. (IV) Nervus trochlearis, iV. tr. the trochlear or patheticus nerve. — Fig. 116 ; 

 PI. I, Fig. 3 ; PI. II, Fig. 3 ; PI. Ill, Fig. 9. Gray. A, 641 ; Quain, A, I, 519. 



This, the smallest of the cranial nerves, arises from the valvula by three fasciculi. 

 The trunk is involved in the pia and easily torn away therewith. 



It passes laterad and then ventro-cephalad between the cerebellum and the hemi- 

 sphere, associates itself with the ophthalmic division of the trigeminus, and emerges 

 therewith by the Fm. lacerum anterius to supply the M. trochlearis (" obliquus superior "). 

 According to the Thesis of C. E. Manierre, this nerve enters the ocular aspect of the mus- 

 cle in the cat, while in man it enters the orbital or ectal aspect. 



§ 1884. (V) Nervus trigeminus, iV. trg.,^he trigeminal or trifacial nerve. — Fig. 116; 

 PI. II, Fig. 3. Gray, A, 647 ; Quain, A, I, 532. 



This is the largest of the cranial nerves and peculiar in several respects. Although 



