XVI 



THE NERVOUS SYSTEM 



295 



separated from the latter by a shallow lateral sulcus. Unlike 

 the cerebral hemispheres, they are closely fused together in 

 the mid'dle line ; on the ventral side, however, they show 

 a well-marked median fissure. Anteriorly they give off the 

 olfactory nerves. 



The Cranial Nerves. — There are ten pairs of nerves in 



FIG. 85. — Diagram of the distribution of the fifth, seventh, ninth, and tenth 

 cranial nerves, the first spinal nerve, and the anterior part of the sympa- 

 thetic. Ao, systemic arch of aorta ; br.pl, brachial plexus ; D.Ao, dor- 

 sal aorta ; du, duodenum ; H , heart ; Hy, hyoid with hy 1 anterior and hy- 

 posterior horns; L, lung; N, nasal bone; On, orbit; Pul, pulmonary 

 artery; Sp.A, splanchnic, or coeliaco-mesenteric artery; St, stomach; 

 Sy, sympathetic ; //, cut end of optic nerve ; V 1 , ophthalmic, V 2 , maxil- 

 lary, and V s , mandibular branch of fifth, or trigeminus nerve; VII 1 , 

 palatine, and VII 2 , hyomandibular branch of facial ; IX, glossopharyn- 

 geal nerve ; X, vagus with Xcd, cardiac, Xgas, gastric, Xlar, laryngeal, 

 and Xpul, pulmonary branches; / Sp, first spinal nerve, or hypoglossal; 

 2 sp-j sp, second to fifth spinal nerves. (From Parker and Parker's 

 Zoology, slight'y modified from Howes.) 



