THE BRAIN, AND COMPARATIVE BEHAVIOUR 377 



and its hereditary nature is due to the fact that the reflex arcs 

 and association-neurons in the thalamus and corpus striatum 



Fig. 172. — Dorsal views of the brains of A, Petromyzon ; B, Scyllium ; C, 

 Gadus ; D, Ceratodus ; E, Triton ; F, Lacerta ; G, Columba ; and 

 H, sheep. (Not all drawn to the same scale.) 



c, cerebellum ; ch, cerebral hemisphere ; /, flocculus ; hb, hindbrain ; 

 mb, midbrain ; ol, olfactory lobe ; on, olfactory nerve ; op, optic lobe ; ot, 

 olfactory tract ; p, pineal ; v, vermis- 



conform to a certain pattern which is the result of development. 

 This also accounts for the fact that instincts are specific, that 



