CERTAIN SETS OF NERVES 



89 



Of these, three, the olfactory, optic, and auditory, are (mostly 

 afferent) nerves of special sense; five, the motor oculi, pathetic, ab- 

 ducens, facial, and hypoglossal, are chiefly efferent or motor nerves; 

 while the remaining four, the trigeminal, glosso-pharyngeal, vagus, and 

 spinal accessory, are of mixed functions special sense, general sensibility, 

 (touch, pain, myesthesia, heat, cold, etc.), trophism, motion, and vaso- 

 motion in various combinations, whose details are not yet in all cases 

 sure. For detailed information as to the cerebral origins, the distribu- 

 tion, and the functions of these complex groups of afferent and efferent 

 nerve-paths the reader is referred to text-books of anatomy and of the 

 physiology of the nervous system. 



FIG. 45 



Brain 



Cerebellum 



Sensory root 



Fibre of ass. 



Afwoui. bundle 



Diagram showing the collection of different sorts of influence by a motor root nerve-cell. 



(Morat.) 



The Spinal Nerves. These are thirty-one in number, on either side 

 of the body. Each arises by two roots, an anterior and a posterior. 

 The former root is mostly motor, vaso-dilator, "secretory," and 

 "trophic"; the latter mostly sensory. Each divides into two trunks, one 

 leading to the tissues of the back, and the other, much the larger, to the 

 remaining parts of the body-trunk and to the limbs. We need do no more 

 than to explain some of the principles of action of these afferent, inward, 

 and efferent, outward, impulses and to summarize for reference purposes 

 the basis of distribution of the motor nerves, showing the sensory dis- 

 tribution so far as it is dermal by an illustration. The process here out- 



