THE EVIDENCE OF THE CENTRAL NERVOUS SYSTEM 13 
each pair gives rise to the nerves of its own segment, and these 
nerves are not nerves of special sense as are the supra-cesophageal 
nerves, but motor and sensory to the segment; nerves by the agency 
of which food is taken in and masticated, respiration is effected, and 
the animal moves from place to place. 
In the vertebrate the central nervous system consists of— 
1. The brain proper, from which arise only the olfactory and optic 
nerves. 
DORSAL 
Spinal canal Neurenteric canal 
Spinal Cord. + Segmental Nerves 
Ami. s 
Infun dubulum VENTRAL 
DORSAL 
Intestine 
Cephalic Stomach : 
Ventral Chain # Ganglia é 
Anus 
? Obophiegiie VENTRAL 
= Com. 
Fic. 8.—VERTEBRATE CENTRAL NERVOUS SYSTEM COMPARED WITH THE CENTRAL 
Nervous System aND ALIMENTARY CANAL OF THE ARTHROPOD. 
A. Vertebrate central nervous system. S. Inf. Br., supra-infundibular brain; 
I. Inf. Br., infra-infundibular brain and cranial segmental nerves; C.Q., corpora 
quadrigemina; Cb., cerebellum; C.C., crura cerebri; C.S., corpus striatum ;' Pn., 
pineal gland. 
B. Invertebrate central nervous system. S. Gis. G., supra-cesophageal ganglia; 
I. Gs. G., infra-cesophageal ganglia; Gs. Com., esophageal commissures. 
2. The region of the mid-brain, medulla oblongata, and spinal 
cord; from these arises a series of nerves segmentally arranged, 
which, as in the invertebrate, gives origin to the nerves governing 
mastication, respiration, and locomotion. 
Further, the vertebrate central nervous system possesses the 
peculiarity, found nowhere else, of being tubular, and the tube is 
of a striking character. In the spinal region it is a small, simple 
canal of uniform calibre, which at the front end dilates to form the 
ventricles of the region of the brain. From that part of this dilated 
