THE EVIDENCE OF THE CENTRAL NERVOUS SYSTEM I * 



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 



Neureateric canal 



H JM I | II p r' 



Spinal Cord « Seomenlal Nerves 



U/un^tulum VENTRAL 



DORSAL 



• ■■'aiopKaju. VENTRAL 



Fig. 3. — Vertebrate Central Nervous System compared with the Central 

 Nervous System and Alimentary Canal of the Arthropod. 



A. Vertebrate central nervous system. 8. 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; Fn.. 

 pineal gland. 



B. Invertebrate central nervous system. <S'. (27s. G., supra-cesophageal ganglia ; 

 I. (Es. G., infra-cesopbageal ganglia; QSs. Com., oesophageal 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 



