SPINAL CORD AS A PATH OF CONDUCTION. 



161 



the cord, the tautomeric tract cells of Van Gehuchten. (b) 

 Those whose axons pass through the anterior white commissure 

 and thus reach the tracts in the white matter of the other side. 

 These are known as commissural cells or the heteromeric tract 

 cells of Van Gehuchten, They form one obvious means for crossed 

 conduction in the cord, (c) Those whose axons divide into two, 

 one passing into the white matter of the same side, the other pass- 

 ing by way of the anterior commissure to reach the white matter 

 of the opposite side — the hecateromeric tract cells of Van Gehuch- 

 ten. (3) The Golgi cells of the second type — that is, cells whose 



l/enTral 



Fig. 73. — Schema of the structure of the cord. — After Lenhossek.) On the right the 

 nerve cells; on the left the entering nerve fibers. Right side: 1, Motor cells, anterior 

 column, giving rise to the fibers of the anterior root; 2, tract cells whose axons pass into 

 the white matter of the anterior and lateral funiculi; 3, commissural cells whose axons pass 

 chiefly through the anterior commissure to reach the anterior funiculi of the other side; 

 4, Golgi cells (second type), whose axons do not leave the gray matter; 5, tract cells whose 

 axons pass into the white matter of the posterior funiculi. Left side: 1, Entering fibers 

 of the posterior root, ending, from within outward, as follows: Clarke's column, posterior 

 column of opposite side, anterior column same side (reflex arc), lateral column of same side, 

 posterior column of same side; 2, collaterals from fibers in the anterior and lateral funiculi, 

 3, collaterals of descending pyramidal fibers ending around motor cells in anterior column. 



axons divide into a number of small branches like those of a 

 dendrite. The axons of these cells, therefore, do not become 

 medullated nerve fibers; they take no part in the formation of 

 the spinal roots or the tracts of white matter in the cord, but 

 terminate diffusely within the gray matter itself. (4) The pos- 

 terior root cells lying toward the base of the anterior columns. 

 These cells have been demonstrated in some of the lower verte- 

 brates (petromyzon — chick embryo), but their existence in the 

 mammal is still a question in some doubt; their axons pass out 

 from the cord by the posterior root and they form the anatomical 

 evidence for the view that the posterior roots may contain some 

 efferent fibers. Some of the groups of tract cells have been given 

 special names — such, for instance, as the dorsal nucleus (Clarke's 

 11 



