THE SPINAL CORD 



529 



ip to the surface of the cord, where it is capped by gelatinous matter, the 

 ^ubstantia gelatinosa. In the lower cervical and thoracic regions a portion 

 :>f the intermediate gray substance projects outward and forms the so-called 

 ateral horn. The gray matter fundamentally consists of a framework of 

 jfine neuroglia supporting blood-vessels, lym- 

 phatics, medullated and non-medullated nerves, 

 and groups of nerve-cells. 



The Nerve-cells. The nerve-cells of the 

 cord are very numerous and they present a va- 

 riety of shapes and sizes in different regions. 

 They are usually arranged in groups which ex- 

 tend for some distance up and down the gray 

 matter, forming columns more or less continuous. 



In the anterior horn two well-marked groups 

 are found, one situated at the anterior and inner 

 angle, known as the antero-median group, the 

 other situated at the posterior and lateral angle 

 and known as the postero-lateral group. In the 

 lower cervical and upper thoracic regions, in the 

 region of the lateral horn, another group of cells 

 is found, known as the intermediate group. In 

 the central portion of the horn there is also a 

 central group. 



The cells of the anterior horns are of large 

 size, nucleated and multipolar. They are the 

 modified descendants of pear-shaped cells, the 

 neuroblasts, which migrated from the medullary 

 tube (see page 9 7 ). In the course of their mi- 

 gration they developed dendrites which form 

 an intricate felt-work throughout the anterior 

 horn. One of the processes, the axon, ap- 

 proached the surface of the cord, penetrated it, 

 grew outward, became covered with myelin and 

 neurilemma, and developed into an anterior 

 root fiber. These nerve-cells, with their den- 

 drites, axons, and terminal branches, J )rm of the sixtl? cervical nerve . B . 



efferent neurons of the first order. The inti- At the mid-dorsal region, c. 



th lumbar 



FIG. 227. SECTIONS THROUGH 



mate histologic and physiologic relationship _At 

 existing between the nerve-cell and the axon is part O f t h e conus meduiiaris. i. 

 revealed by the degenerative changes which ^^-ts^^An^nor^ 

 arise in the latter when separated from the ssure ^ Central canal _ ( Uor . 

 former. The cell apparently determines the rz y "Anatomy," after Schwdbe.) 

 nutrition of the axon and may be regarded as 



trophic in function. Some of the cells of the anterior horn send their axons 

 into the immediately surrounding white matter of the same side, after which 

 they divide into two branches, one passing up, the other down, the cord, 

 to reenter the gray matter at different levels. They are probably asso- 

 ciative in function. Other cells send their axons into that portion of the 

 white matter on the same and opposite sides known as Gower s 

 lateral tract (Fig. 228). 



