74 



PHYSIOLOGY AND MORPHOLOGY OF ANIMALS. 



tion, which determine intellect quite as much as or more 

 than size. Perhaps it might be well to say here, for the 



comfort of those who 

 wear small-sized hats, 

 that brain power does 

 not depend on size 

 alone, any more than 

 bodily strength de- 

 pends on weight alone. 

 In both cases it is a 

 product of two factors, 

 viz., size and fineness 

 of organization, and 

 the latter is the more 

 important factor. 



Brains of Extinct 

 Species. — It is a cu- 

 rious and significant 

 fact that in each of 

 these classes extinct 

 species are remarka- 

 ble for the smallness 

 of their brains. There 

 has been a gradual in- 

 crease in the size of 

 the brains of animals 

 in each of these classes 

 from their first intro- 

 duction until now. To 

 give one example, the 

 extinct Cretaceous bird Ichthyornis was about the size 

 of a tern, but its brain was hardly one quarter as large 



(Fig- 39)- 



2. Relative Amount of Gray Matter. — The gray 



matter is the generator, the white fibers only transmitters of 



Fig. 39. — A, outline of the skull and brain 

 cavity of Ichthyornis victor (after Marsh), 

 seen from above. (Five sixths natural 

 size.) B, outline of the skull and brain 

 cavity of Sterna cantiaca (after Graelin), 

 same view. (Natural sizei) ol, olfactory 

 lobes ; c, cerebral hemispheres ; op, optic 

 lobes : cb, cerebellum. 



