THE SPINAL CORD AS A CONDUCTING PATH 607 



tudinal axis of the cord. Their axons tend obhquely outward into 

 the so-called direct cerebellar tract of the lateral white matter. Some 

 of these processes also pass into the fasciculi next to the posterior 

 median fissure. Posterior to this group of cells, constituting the 

 so-called Clarke's vesicular column, we find a few ceils distributed 

 in an irregular manner through the posterior horn. The cells of the 

 sensory fibers forming the posterior roots, are, of course, situated 

 outside the cord, in the spinal ganglia. 



When considered from the standpoint of gross and minute anatomy, 

 the white matter of the spinal cord presents itself as three funiculi 

 which in turn are divided into several fascicuh. The physiologist, 

 however, is more directly concerned with the function of these col- 

 lections of nerve fibers and hence, his unit is the tract, i.e., bundles 

 of fibers possessing an identical action. But as several of these 

 tracts have clearly defined anatomical boundaries, these terms are 

 frequently used interchangingly. As far as the cells of the gray 

 matter are concerned, is is important to determine the tracts to which 



Fig. 299. — Spinal Ganglion op an Embryo Duck; Composed of Diaxonic Nerve-cells. 



{van Gehuchten.) 



these cells are functionally related. Upon this basis we may divide 

 them into two main groups, namely, local and general. As the former 

 are intended to establish a close relationship between the cells situated 

 in different parts of the gray matter and at different levels of the cord, 

 they are associative (tautomeric) or commissural (heteromeric) in 

 their nature. In this class should be placed the cells of Clarke's 

 column, because they are tributary elements to the direct cerebellar 

 and posterior tracts. The same is true of the cells of the median 

 group, because they send their axons across the middle line to the 

 opposite gray matter and thus become commissural in their nature. 

 Another type of associative cell is the cell of Golgi which is found 

 chiefly in the posterior horn. Its axon does not pass far away from 

 the cell-body, but ramifies extensively to establish connections with 

 neighboring cells at any level of the cord. 



The group of the general cells is made up of those cells which are 

 concerned with bringing the cord into relation with the higher centers 

 as well as with the peripheral end-organs. Chief among these 

 are the large ganglion cells in the anterior horn, measuring 57 



