THE NERVOUS SYSTEM OF MAN. 40 



back, like a bounding ball, to the appropriate muscle 

 without rising into consciousness at all. To it is as- 

 signed the control of all those wholly unconscious and 

 involuntary movements — such as those of the heart, the 

 stomach, and the intestines — so necessary to the con- 

 tinuance of bodily life. 



The gray matter of the cord is continuous with the 

 gray matter of the basal part of the brain, especially of 

 the medulla, but entirely separated from the exterior 

 gray matter of the cerebrum and cerebellum. The 

 function of the gray matter of the medulla, like that of 

 the spinal cord, is wholly reflex or automatic; that of 

 the thalamus, semiautomatic. Thus, speaking generally, 

 as we go headward and cerebrumward the function of 

 gray matter becomes higher, less automatic, more dis- 

 tinctly conscious, and voluntary. 



SECTION III. 



Nerves. 



We have already said that there are forty-three pairs 

 of axial nerves — i. e., twelve intercranial and thirty-one 

 extracranial or spinal. 



Cranial Nerves. — These all come from the inter- 

 cranial continuation of the axis at the base of the brain, 

 and not from the great outgrowths of the cerebrum and 

 cerebellum, unless we except one, the olfactory, coming 

 from the cerebrum. They all pass through holes in the 

 base of the skull, and are distributed, with two excep- 

 tions, to the head and face. Several of them are nerves 

 of special sense. The cranial nerves, on account of 

 their higher and more differentiated functions, have 

 all of them, in addition to their ordinal, also special 

 names. In the order of their position, beginning in 

 front, they are : 



