116 



HUMAN PHYSIOLOGY 



or smell parts in front, the forebrain coming next in 

 order, whilst there respectively succeed the middle 

 brain and the hind brain. As we advance towards 

 the reptiles, we discover that the fore brain tends to 

 overshadow by its greater prominence the middle 

 brain, and when we arrive at the bird, we find this 



Fig. 31. THE BASE OF THE BRAIN 



Showing the cerebellum behind, and the origin 



of the spinal cord. The olfactory lobes lie in 



front, and the optic nerves behind them. 



part with its disproportionate size arising from 

 increased growth, and also with the enlargement of 

 the hind brain, completely covers the middle brain. 

 In the lower quadrupeds much the same development 

 is seen. As we advance a tendency is shown for 

 the fore brain to increase in size, and to grow not 



