102 



EXPERIMENTAL PHYSIOLOGY 



the division into two parts by a deep anterior, and shallow 

 posterior fissure. Note also two fissures in each half (an- 

 terior and posterior lateral) through which the central gray 

 mass reaches the surface. The gray masses in each half of 



Posterior 



FIG. 50. 



the cord may be seen to be united by a commissure that 

 incloses the central or neural canal. Note the cellular char- 

 acter of the gray matter. The gray matter that forms the 

 posterior horns forms the core of spinal nerves of the sort 

 called afferent. The anterior horns form the core of effer- 

 ent nerves. (Afferent nerves carry messages to the cord, 

 efferent away from it.) The white matter covers these and 

 they unite outside in a common spinal nerve. (See Fig. 50.) 

 For structure of a neuron, see Ex. XXVIII. 



