ANATOMY, PHYSIOLOGY, OF NERVOUS SYSTEM. 455 



cord, in the gray matter of the anterior horns. This differ- 

 ence of position is, of course, physiologically a secondary 

 one. 



The sensory cranial nerves find their counterparts of the 

 spinal root ganglia in the sensory ganglia which they pos- 

 sess. Such, for instance, as the Gasserian ganglion of the 

 fifth cranial nerve. 



It simplifies the conception of the sympathetic system, 

 to look upon the sympathetic ganglia lying along the spinal 

 cord as a second set of spinal root ganglia containing sen- 

 sory and possibly motor neurons, which in this case reach 

 from the spinal cord to the viscera, instead of to the body 

 wall and skin as in the case of the spinal root ganglia proper. 

 This conception of the sympathetic ganglia as spinal root 

 ganglia lends a unity to the entire nervous system, doing 

 away at once with the too general notion that the sympa- 

 thetic system is a special system only incidentally connected 

 with the spinal cord. 



THE MEDULLA. 



In the medulla the general arrangement of gray and 

 white matter found in the cord is materially varied from for 

 several reasons. In the first place, the decussation of the 

 motor and sensory fibers displaces the gray matter. In 

 addition to that we find here many new centers. In the 

 medulla are located, for instance, the center governing 

 respiration, that governing the temperature of the body, 

 that governing the vascular supply, and others. In addi- 

 tion to that we find here much gray matter, the cells of 

 which are probably the second neurons of sensation just 

 described. Here, also, are a number of centers connected 

 with the nerves of the special senses. The exact location 

 of these centers is omitted from this elementary discussion 

 as being too complicated. There remains, therefore, for 

 further description the arrangement of fibers and centers in 

 the cerebellum and cerebrum. 



