SUPPOMT, MOTION, AND SENSATION 



347 



Before going further with a consideration and (hseussiou of the 

 human nervous system, a comparison of brains of (Hfferent verte- 



amphibian 



rsptile. 



Cerebrtc 



'bineo.l 

 bocL' 



opLic 



lobe,' ,, 

 c^.r-ebe-llum' 



optic 

 lobe 



mccCitlla. 



snake^ 



brates should be made 

 for the sake of clearness. 

 Remembering that the 

 brain of a fish is not 

 folded upon itself as is 

 the brain of a mammal, 

 it is easy to see that the 

 introduction of flexures 

 tends towards greater 

 compactness. Another 

 outstanding develop- 

 ment is the increase in 

 size of some of the re- 

 gions of the brain. In 

 lower forms, the domi- 

 nating portions of the 

 brain from the stand- 

 point of mass are the 

 optic lobes of the mid- 

 brain and the medulla 

 oblongata, and, as 

 might be inferred, both 

 the cerebrum and cere- 

 bellum are quite small. 

 In the higher mammals, 

 however, these organs become two of the most important centers 

 in the brain, increase in the size of the cerebrum being in direct pro- 

 portion to the intelligence of the animal. 



An examination of a few of the more important landmarks of the 

 divisions of the brain in order to secure a general idea of the function- 

 ing of each of these parts will furnish a background for the discussion 

 of the '' Display of energy." 



The Parts of the Vertebrate Brain 



The Cerebrum or Telencephalon. As the adult condition is 

 approached, certain other characteristic structures appear. From 

 the anterior portion of the cerebrum grow the paired olfactory lobes. 

 In lower xertebrates these may extend into expanded olfactory hulhs. 



d-'CX.t-' 



Representative vertebrate brains. o.L, olfactory 

 lobes. W hat reffions increase noticeably in mass from 

 fish to manmials ? How are these changes correlated 

 with the shift from water to land:* (After Guyer.) 



