ARRANGEMENT OF NERVE CELLS IN THE SPINAL CORD 



513 



are small and branched, and each has an axis-cylinder process passing cff; 

 but these processes do not pass into the posterior nerve roots. The groups 

 are two at least in number, viz., a, in connection with the edge of the gray matter 

 externally, where it is considerably broken up by the passage of bundles of 

 fibers through it, and called the lateral reticular formation ; and b, in connection 

 with a similar reticular formaticn, more at the tip of the gray, known as the 

 posterior reticular formation. 



A group of cells, 3, figure 360, is situated at the base and median side of the 

 posterior cornu. It is formed of fairly large cells, fusiform in shape, and 

 constitutes the posterior vesicular column, or Clarke's column. It extends 

 from the seventh cervical to the third lumbar segment. On the outer por- 

 tion of the gray matter, midw r ay between the anterior and posterior cornua, 



FIG. 360. Section of Spinal Cord, One Half of Which (Left) Shows the Tracts of the White 

 Matter, and the Other Half (Right) Shows the Position of the Nerve Cells in the Gray Matter. 7, 

 ip, 9, and 3 are tracts of descending degeneration; i, 4, 6 and 8, of ascending degeneration. Semi- 

 diagrammatic. (After Sherrington.) 



is a group of cells, known as the cells of the lateral gray column. These are 

 small and spindle-shaped, and are more or less marked in the lumbar region, 

 as well as in the thoracic region, 5, figure 360. 



Besides these groups, which have their names largely on account of their 

 location, there are distributed throughout the gray matter a very large number 

 of other cells, which are known as intrinsic cells. These send out axones 

 which pass into the adjacent ground bundles of the same or of the opposite 

 side, and pass up and down the cord, to enter the gray matter again. They 

 connect by their end-brushes with cells at different levels of the cord. 



The function of these connecting cells, or intrinsic cells, is to unite the pos- 

 terior and anterior regions of the cord, to serve as conductors between the 

 lateral halves, or to connect segments at different levels. They are also dis- 

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