A STUDY OF THE NERVOUS SYSTEM 289 



Brain of Salmon. 



Brain of Frog. 



Brain of Alligator. 



Brain of Pigeon. 



Lai 



Brain of Dog. 



KO. 

 Brain of Man. 



FIG. 130. A Comparison of Brains (all represented as though they were 

 of the same size). Left side view (except alligator's brain). 



HH= cerebellum. 



L.ol = olfactory lobe. 



Med = spinal cord. 



MH= midbrain (optic lobes). 



NH= medulla. 



Po = pons. 

 VH= forebrain. 

 I-XII = cranial nerves. 

 1, 2 = spinal nerves. 



same size. The following striking differences are seen as 

 one follows the series from the fish to man : 



(1) There is a gradual increase in the size of the cerebral 

 hemispheres, until in man they constitute three fourths of 

 the whole brain. The surface of the hemispheres in all the 

 lower forms is smooth, and hence the cortex is usually small 



