I 10 



The Nervous System 



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

 small olfactory lobes, which 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 brain does 

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



-VII 



ML 



FIG. 78. FIG. 79. FIG. 80. 



FIG. 78. Brain of a Shark (Squatina squatina L.). (After Dean.) 



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



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



E. Epiphysis. V4. Fourth ventricle. 



T. Thalamencephalon. M. Mesencephalon (optic lobes). 



II. Second cranial nerve. MT. Metencephalon (medulla). 

 IV. Fourth cranial nerve. EP. Epencephalon (cerebellum). 



FIG. 79. Brain of Chimcera 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 



