NEKVOUS SYSTEM. 

 FIG. 66. 



A 



61 



Brain or principal portion of the cerebro-spinal system of a Rabbit. Upper surface 

 on the right, lower on the left. 



A, olfactive lobes ; B, cerebral hemispheres ; D, cerebellum ; ol, olfactive lobes ; op, 

 optic nerve; TOO, motor oculi; cm, corpora mamillaria ; cc, crus cerebri; pv, pons va- 

 rolii; pa, patheticus; tri, trifacial; ab, abducens; fuc, facial; au, auditory; vag, vagus; 

 , spinal accessory ; hyp, hypoglossal. 



viscera. The nerves of this system extend to the vital 

 organs, as the stomach, heart, lungs," liver, intestines, etc. 



The nerves originating in the cerebro-spinal system of the highest 

 mammal, namely, Man, amount to forty-three pairs twelve pairs 

 arising within the cranium, and leaving that cavity by apertures in the 

 cranial bones, and thirty-one pairs arising from the spinal cord, and 

 leaving by apertures situated between the vertebratae. Each of these 

 pairs is composed of a great number of extremely fine threads or fibers 

 inclosed in a sheath. At their origin, the fibers which make up the 

 nerve are called roots, and, in the case of the spinal nerves, are grouped 

 into anterior and posterior roots. On the posterior root there is a gan- 

 glion through which the filaments pass and after that unite with the 

 anterior root. 



The brain itself is insensible, not feeling even when ir- 

 ritated or cut ; but it is nevertheless the seat of sensation, 



