SENSORY PATHS IN THE CORD 245 



longed upward in the pyramidal tracts. The number of 

 fibers in these roots is much larger than in the pyramidal 

 tracts, and consequently some of them must end (originate) 

 directly in the cells of the anterior cornua. Furthermore, it 

 seems that some fibers pass from the anterior nerve roots 

 directly into the pyramidal tracts without being interrupted 

 by motor cells. 



The column of Turck and the crossed pyramidal tract 

 are, therefore, the motor paths in the cord. 



Fibers entering the cord by the posterior roots send pro- 

 longations both upward and downward in the gray matter of 

 the cord, and communicate by end arborizations with the 

 small sensory cells in the posterior cornua and with cells in 

 several other localities. (See Figs. 77, 84.) Reference to 

 Fig. 77 will show that the connection of the anterior nerve 

 fibers with the gray matter of the cord is simple, while that 

 of the posterior is comparatively complex, i, 2, 3, 4 are an- 

 terior horn cells. Each of these gives rise to an efferent 

 fiber, one of which (A) is shown distributed to a muscle 

 (M). Each of these cells also is surrounded by the end ar- 

 borization of a fiber (P) from the cortex. 



A fiber from the posterior root is also shown. It origin- 

 ates in a cell of the sensory ganglion (G). It bifurcates, 

 one branch going to the surface (S), the other enters the 

 cord and itself bifurcates. The branch (E) is short and 

 arborizes around a small cell (Pi) in the posterior cornu, 

 from which a new axis cylinder arises to arborize around 

 the anterior horn cell (4). The other branch (D) travels 

 upward in the posterior column of the cord. A collateral (5) 

 is seen going to the anterior horn cell (2), one to the pos- 

 terior horn cell (P2) and another to a cell (C) in the inner 

 base of the posterior cornu (in Clarke's column) ; from C 

 an axis cylinder enters the direct cerebellar tract. The 

 main fiber (8) may terminate in the gray matter of the 

 cord above, or in the medulla. Impressions brought thus to 

 the cord are carried to the opposite side and pass up 



