460 



THE ORGANS 



of the cell. In the medium cells more chromophilic bodies are present. The 

 cells of Clarke's column have a considerable number of chromophilic bodies 

 arranged near the periphery of the cell. The root cells are richest in chromo- 

 philic substance (for further details see Chap. X). In general it seems that 

 the intermediate neurones belonging to efferent paths {i.e., acting on periph- 

 eral motor neurones) have the definite, clear-cut, coarse chromophilic granules 

 characteristic of the peripheral motor neurones; while the neurones forming 

 parts of afferent paths have the fine, indefinitely grouped granules character- 

 istic of the ccrcbro-spinal ganglionic neurones (Jacobsohn and Malone). 



Blood-vessels (Fig. 322. — ) Study the arrangement and structure of the blood- 

 vessels of the cord and pia. There are three principal longitudinal arteries, 

 the anterior spinal artery given ofT from the vertebral arteries near their union 



Posterior spinal artery 



Region sup- 

 plied by sulco- 

 commissurae 

 artery 



Column cells 



Anterior spinal artery 

 (giving off a sulco-commissural artery) 



Root cells 



Fig. 322. — Schematic transverse section of Cord, Showing General Distribution of 

 Blood-vessels (leftj and Nerve-cells (right) (Bing). Root-cells; i, postero-lateral group; 

 2, antero-lateral group; 3, antero-medial group; 4, central group; 5, postero-medial 

 group. The broken black lines on the surface of the cord are portions of the vascular 

 network in the pia mater. 



into the basilar artery, and two posterior spinal arteries, given off also from the 

 vertebral arteries. These arteries are reenforced by small arteries passing to the 

 cord along the dorsal and ventral roots and form an arterial network in the pia 

 mater. From the network terminal {i.e., non-anastomosing) branches enter 

 the cord, supplying all parts except the ventral horn and column of Clarke. 

 The latter are supplied by branches from the anterior spinal artery which pass 

 dorsally in the ventral sulcus {sulco-commissural arteries) and enter the cord 

 alternately to right and left. They then break up into a rich capillar}- network 

 in the ventral horn, supplying also a branch to the column of Clarke. The veins 

 of the cord also form a plexus in the pia mater. Larger posterior median and ati 

 terior median veins can be distinguished. Portions of the above vessels can be 

 seen, cut in various planes in the pia and in the cord. The general appearance 

 and structure, of the blood-vessels, including capillaries, should be noted in the 

 various methods of staining. 



