THE NEKVOUS SYSTEM 



267 



cerebral hemispheres, which in man grow to such proportions 

 upwards and backwards as to overhang and completely cover 

 the other structures on the dorsal side. But even these large 

 masses of nervous tissue, no less than the smaller cerebrum 

 of the frog, are composed entirely of the gray and white 

 matter forming the walls of the lateral ventricles. 



By comparing the brain of a frog (Fig. 105) with those 

 of the rabbit, cat, and monkey (Fig. 166), and finally with 



FIG. 108. Median longitudinal section of the human brain 



A, B, C, D, L, convolutions of the median surface of the cerebrum ; E, F, the 



cerebellum, showing in the plane of section the inner white matter and the outer 



gray matter ; H, the pons Varolii ; If, the bulb 



the human brain (Figs. 104, 107, 108), a fairly good idea 

 may be had of the increasing complexity of the brain as we 

 pass from the lower to the higher animals. Especially note- 

 worthy is the greater relative prominence of the cerebrum. 

 In the frog this organ is small and inconspicuous ; in the 

 rabbit it is much larger, but its surface is smooth ; in the cat 

 there is a further increase in size, and the surface is thrown 



