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 middle 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 /zy 1 anterior and hy^ 

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

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

 Sy, sympathetic ; //, cut end of optic nerve ; J 71 , ophthalmic, V 2 , maxil- 

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

 palatine, and VI1'~, hyomandibular branch of facial ; IX, glossopharyn- 

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

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

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

 Zoology, slightly modified from Howes.) 



