4o8 



COLLEGE ZOOLOGY 



Nervous System. — The nervous system of vertebrates is 

 more complex than that of any other animals. It comprises a 

 central nervous system consisting of the brain and spinal cord, 

 a peripheral nervous system consisting of the cerebral and spinal 

 nerves, and a sympathetic system. The brain is made up of three 

 primary vesicles, a fore-brain, mid-brain, and hind-brain. The 

 fore-brain is thought to correspond to the cerebral vesicle of 



e.eort 



Fig. 349. — Diagram of the spinal cord showing the paths taken by nervou^ 

 impulses. The direction of the impulses is indicated by arrows, c.c, central 

 canal; col, collateral fibers; c.cort, cell in the cerebral cortex; eg, smaller 

 cerebral cell; d.c, cells in dorsal horn of gray matter; d.r, dorsal root; g, gan- 

 glion of dorsal root; g.c, ganglion cell in dorsal ganglion; g.m, gray matter; 

 M, muscle; m.c, cell in medulla oblongata; m.f, motor fiber; 5, skin; s.f, sen- 

 sory fiber; sp.c, spinal cord; v.c, cells in ventral horn of gray matter; 

 v.r, ventral root; w.m, white matter. (From Holmes, after Parker.) 



Amphioxus (Fig. 343, br). The fore-brain usually gives rise to a 

 pair of cerebral hemispheres, the mid-brain to a pair of optic lobes, 

 and the hind-brain to the cerebellum and medulla oblongata. 

 The spinal cord is a thick tube directly connected with the brain; 

 it passes through the neural arches of the vertebral column. 



The peripheral nervous system consists of ten to twelve pairs 

 of cranial nerves and a number of pairs of spinal nerves. The 

 origin, distribution, and function of the cranial nerves are 

 indicated in Table XIV. 



The spinal nerves arise from the spinal cord in pairs, one on 



