450 



THE ORGANS 



pallium, in the midbrain, cerebellum(?), and various parts of the 

 segmental brain. The axones of these cells pass down the cord, 

 forming the descending fibre tracts of the cord (p. 470). Collaterals 

 and terminals of these fibres enter the gray matter of the cord to ter- 

 minate there. 



/ 

 Fig. 316. — Transverse Section through Spinal Cord and Posterior Root Ganglia of 

 an Embryo Chick. (Van Gehuchten.) a, Spinal ganglion, its bipolar cells sending their 

 peripheral processes outward to become fibres of the mixed spinal nerve (/), their central 

 processes into the dorsal columns of the cord as the dorsal root fibres (b) ; within the pos- 

 terior columns these fibres can be seen bifurcating and sending collaterals into the gray 

 matter of the posterior columns, one collateral passing to the gray matter of the opposite 

 side. The few efferent fibres of the dorsal root (c) are disproportionately conspicuous. 

 The large multipolar cells of the ventral horns are seen sending their axones (d) out of the 

 cord as the ventral root fibres (e) which join the peripheral processes of the spinal gang- 

 lion cells to form the mixed spinal nerve (/) ; col, collateral from axone of ventral horn cell. 

 Dendrites of the anterior horn cells are seen crossing the median line in the anterior com- 

 missure. About the centre of the cord is seen the central canal; dorsal and ventral to 

 the latter some ependymal cells stretching from the canal to the periphery of the cord. 

 (Golgi Method.) 



I 





(3) Root Cells — Motor Cells of the Anterior Horn 



The course of the axones of these cells has been described (p. 447). 

 The bodies are described on pp. 457 and 458. 



(4) Column Cells. 



These are cells which lie in the gray matter of the cord and send 

 their axones into the white columns or funiculi (see p. 456) where 

 they either bifurcate or turn up or down, becoming longitudinal 

 fibres. Some of the cells send their axones into the white matter of 

 the same side of the cord. These are known as tautomeric cells 

 (Fig. 317, 3). Others send their axones as fibres of the anterior 

 commissure to the white matter of the opposite side of the cord — 



