THE NERVOUS SYSTEM OF MAN 15I 



brain to optical activities, and just back of this 

 region is the auditory area. This differentiation 

 is so obvious that these regions are often desig- 

 nated as the "nose-brain," "eye-brain" and the 

 "ear-brain." There is nothing suggestive of the 

 complicated cerebrum of mammals. (Fig. 51.) 



The amphibians, of which the frog is a type, 

 begin to show a slight modification in the region 

 of the brain just back, of the "nose-brain" but the 

 change is slight. Hardly more can be claimed 

 for the reptiles although the turtle has a con- 

 spicuous mass of nerve cells in the floor of the 

 forebrain. (Fig. 52.) 



In all of the fishes, amphibians and reptiles 

 the spinal cord is similar and does not exhibit any 

 marked specializations. The brain, however, 

 shows that first one region then another is the 

 supreme and final arbiter, with the control grad- 

 ually moving toward the anterior end. This im- 

 portant generalization is only evident after one 

 has made a technical study of the fiber tracts 

 within these several parts. The medulla oblon- 

 gata remains about the same in all. It is a very 

 important region for two reasons: i. It contains 

 an important relay connection between the spinal 

 cord and brain; 2. From it arise seven of the ten 

 important cranial nerves. All taste and hearing 

 nerves enter the nervous system through the me- 



