Chap. 16 CONDUCTION AND COORDINATION NERVOUS SYSTEM 



305 



The medulla is the entrance and exit way of nerve impulses to and from 

 the spinal cord and brain and to and from the last six pairs of cranial nerves, 

 including the widely effective vagus nerves. It is the center of the autonomic 

 control of important body -functions such as respiration and the rate of the 

 heart beat. 



Table 16.3 



Principal Structures of the Adult Human Brain with Their 

 Locations in the Basic Divisions 



Features of the Human Brain 



The history of ihe cerebral hemispheres of vertebrates is one of the most 

 spectacular in comparative anatomy. It begins with them as smooth paired 

 outgrowths of the forebrain, the centers of olfactory sensation in the nose 

 brain of fishes. Later with the adoption of land life, animals had to clamber 

 and creep, and their cerebral lobes became large and important centers of 

 sensory correlation. Finally, with the mammals, the same lobes became a 

 great superstructure reared on the old primitive nervous system. This newer 

 part of the brain is the center of the nervous functions which in man have 

 been developed far beyond those of any other animal. 



The brain is a bilaterally symmetrical organ that acts as a unit in the inver- 

 tebrates as well as in the vertebrates. The action of the hind legs of a grass- 

 hopper is as well timed for a take-off as that in the hind legs of a kangaroo. 



Cerebrum. In contrast to its smoothness in other vertebrates the surface 

 of the mammalian cerebrum is usually increased by fissures and by folds 

 called convolutions (Fig. 16.21). The fact that these convolutions give more 



