ijQ The Nervous System 



of the higher animals. In front of the cerebrum lie the two 

 small olfactory lobes, Avhich receive the large olfactory nerve 

 from the nostrils. From its lower surface is suspended the hy- 

 pophysis or pituitary gland. 



In most of the bony fishes the structure of the bram does 

 not differ materially from that seen in the perch. In the stur- 



Fourth ventricle. 

 Mesencephalon (optic lobes). 

 Metencephalon (medulla). 

 Epencephalon (cerebellum). 



Fio. 78. Fig. 79. Fig. 80. 



Fig. 78. — Brain of a Shark (Squatina squaUna L.). (.\fter Dean.) 



I. First cranial nerve (olfactory). V. Fifth cranial nerve. 

 P. Prosencephalon (cerebrum). VII. Seventh cranial nerve. 

 E. Epiphysis. V-i. 

 T. Thalamencephalon. M. 



II. Second cranial nerve. MT. 

 IV. Fourth cranial nerve. EP. 



Fig. 79. — Brain of ChinKcra monstrosa. (After Wilder per Dean.) 



Fig. 80. — Brain of Protopterus annectens. (After Burckhardt per Dean.) 



geon, however, the parts are more widely separated. In the 

 Dipnoans the cerebral hemispheres are united, while the optic 

 lobe and cerebellum are very small. In the sharks and rays the 

 large cerebral hemispheres are usually coalescent into one, and 

 the olfactory nerves dilate into large ganglia below the nostrils. 

 The optic lobes are smaller than the hemispheres and also coa- 

 lescent. The cerebellum is very large, and the surface of the 



