296 



COORDINATION AND SENSATION 



Spinal 

 nerve 



neurons, the cell-bodies of which are in the gray matter ot 



the cord. 



The first convey impulses to the cord and are called 



afferent neurons ; 1 the second convey impulses from the 



cord and are known as efferent neurons. Thus, by form- 

 ing a part of the 

 nerve pathways 



. between the skin 



and the brain, 

 the dorsal divi- 

 sions of these 

 nerves aid in the 

 production of 

 FIG. 135. Connection of spinal nerves with feeling' and by 



the cord. On the right is shown a nerve pathway , , . 



i i A j- r nT- n. completing path- 



from the skin to the muscle. A division of this path- 

 way reaches the brain. w a.VS to the mus- 



cles, the ventral 



divisions aid in the production of motion (Figs. 129, 135, 

 and 141). 



The Cranial Nerves. From the under front surface of 

 the brain, twelve pairs of nerves emerge and pass to the 

 head, neck, and upper portions of the trunk. These, the 

 cranial nerves, have names suggestive of their function or 

 distribution and, in addition, are given numbers which indi- 

 cate the order in which they leave the brain (Fig. 136). 

 Unlike the spinal nerves, the cranial nerves present great 

 variety among themselves, scarcely any two of them being 

 alike in function or in their connection with different parts 

 of the body. Several of them have to do with the special 

 senses, and are for this reason very important. They 



1 In general, afferent neurons or fibers are those that convey impulses toward 

 the central nervous system (brain and cord), while efferent neurons or fibers are 

 those that convey impulses from the central system. 



