3 



THE NERVOUS SYSTEM 



a transverse fold projecting into the third ventricle from the membranous roof 

 (Fig. 11), and consists of a median unpaired portion, and of the two cerebral 

 hemispheres with their olfactory bulbs. The hemispheres are the evaginated 

 portions of the telencephalon and are partially separated from each other by a 



Olfactory bulb 



Olfactory nerve 



(n.I) 

 Somatic area 



r. ophthal. superfic. V 

 r. ophthal. superfic. VII 



n. terminalis 



r. ophthal. profundus V 



Optic nerve (n. II) 



r. maxillaris V 

 r. mandib. V 



Supra-orbital trunk 



Infra-orbital trunk 

 Ganglion V 

 r. palatinus VII 

 Gang, geniculi VII 

 Gang, later. VII 

 r. prespirac. VII 



Spiracle 



r. hyomandib. VII 



n. IX 

 n. X 



r. lateralis X 



r. branchialis X 

 r. intestinalis X 



Fig. 13. Diagram of the brain and sensory nerves of the smooth dogfish, Mustelus canis, 

 from above. Natural size. The Roman numerals refer to the cranial nerves The olfactory 

 part of the brain is dotted, the visual centers are shaded with oblique cross-hatching, the acoustico- 

 lateral centers with horizontal lines, the visceral sensory area with vertical lines, and the general 

 cutaneous area is left unshaded. On the right side the lateral line nerves are drawn in black, the 

 other nerves are unshaded. (From Herrick's Introduction to Neurology.) 



median sagittal fissure, which has been to a large extent obliterated by the 

 fusion of their median walls. The shape of the lateral ventricle and the position 

 of the interoentricular foramina are shown in Fig. 9. From the lateral side of 

 the rostral end of the hemisphere there projects forward the long and slender 

 olfactory tract with a terminal enlargement, the olfactory bulb. This lies in 



