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HANDBOOK OF PHYSIOLOGY. 



.each gives rise to an axis-cylinder process which passes out in the 

 anterior nerve-root. These cells are everywhere conspicuous, but are 

 particularly numerous in the cervical and lumbar enlargements. In these 

 districts they may be divided into several groups (i.) a group of large 

 cells close to the tip of the inner part of the anterior cornu all the cells 

 of the anterior cornu in the dorsal or thoracic region are said to belong 

 to this group; (ii.) several lateral groups (2, , Z>, and c, fig. 353) on 

 the outer side of the gray matter, and (iii.) a certain number of cells at 

 the base of the inner part of the anterior cornu particularly well marked 

 in the thoracic region, (b) Cells of the posterior cornu these are not 

 numerous; they are small and branched, and each has an axis-cylinder 



Fig. 352. 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, 

 10, 9 and 3 are tracts of descending degeneration, 1, 4, 6 and 8, of ascending degeneration. Semi- 

 diagrammatic. (After Sherrington.) 



process passing off; but these processes do not pass into the posterior 

 nerve-roots. The groups are two at least in number, viz., (i.) in con- 

 nection with the edge of the gray matter externally, where it is consider- 

 ably broken up by the passage of bundles of fibres through it, and called 

 the lateral reticular formation; and (ii.) in connection with a similar 

 reticular formation, more at the tip of the gray matter of the posterior 

 cornu; this is known as the posterior reticular formation. 



A group of cells (No 3, fig. 352) is situated at the base and me- 

 dian side of the posterior cornu. It is formed of fairly large cells, fusi- 

 form in shape, and constitutes the posterior vesicular column, or Clarke's 

 column. It extends from the upper lumbar to the lower cervical region. 

 On the outer portion of the gray matter, midway between the anterior 

 and posterior cornua, 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 



