THE LOWER VERTEBRATA. 185 



large cavities. The olfactory lobes lie well to the side 

 and are joined to the small cerebral lobes by a very 

 wide stalk. The thalamencephalon has a thin, flat roof, 

 from which a long stalk runs forward to the pineal, which 

 lies near the skin, as in the frog. Ventrally, it forms 

 an infundibulum whose sides are thickened and called the 

 lobi inferiores ; while at its end is the pituitary body, with 

 a pair of thin -walled sacs (sacti vasculosi), developed at 

 its sides. The optic lobes resemble those of the frog, but 

 the cerebellum is very large and laps over them. Behind 

 it comes the usual thin roof to the fourth ventricle ; but 

 at the sides of this are a peculiar pair of hollow projections, 

 called the " restiform bodies " (a term applied in human 

 anatomy to the posterior peduncles of the cerebellum, which 

 are not homologous with these structures of the dogfish), 

 On the ventral surface, crura, pons and bulb are all much 

 alike and pass back with little change into the spinal 

 cord. 



The small size of the cerebral lobes betokens a low grade 

 of intelligence, and still more striking than any matter 

 of size is the apparent entire absence of the characteristic 

 pyramidal cells of the cortex of higher types cells specially 

 concerned with the association of ideas. We may therefore 

 expect that memory and the capacity for education are either 

 quite absent or in a most rudimentary state. The habits 

 of the dogfish are not such as to make easy the study of its 

 psychology, but what 

 is known of other 



i /. , 



fishes confirms the 



-,-,,. i. 



deductions from 

 brain-structure. On 



large size of the 

 cerebellum, as con- 

 trasted with its small 



,< . Fig. 98. MEDIAN LONGITUDINAL SECTION 



Size in the irog, IS OF BRAIN OF DOGFISH. 



readily understood. 



Compare their respective shapes in transverse section (e.g. 

 figs. 66 and 88), and it will be seen that the laterally 

 compressed and swimming dogfish has great use for the 



