THE NERVOUS SYSTEM 2QQ 



down from the brain, but none the less many such reflexes 

 are often performed without our knowing it and they con- 

 tinue to be performed if the upper part of the cord is injured 

 or paralyzed so that the lower part of the body is no longer 

 under voluntary control. Reflex acts are performed by 

 way of the brain and other nerve centers as well as by the 



PIG. 213. Lower side of brain. A, C, lobes of the cerebrum; B, 

 olfactory tracts; D, crossing of the optic nerves; H, M, cerebellum; N, 

 medulla; R, pons. (After Leidy.) 



spinal cord. Coughing, sneezing and winking are some of 

 these and they are often performed quite independently 

 of our will. 



Man is remarkable among animals for the great size of 

 his brain. The largest part of the brain consists of the two 

 cerebral hemispheres which are the organs especially con- 

 cerned with voluntary action and the power of thought. 



