608 STRUCTURE OF THE SPINAL CORD. [CH. XLII. 



(b) Cells of the posterior cornu these are not numerous ; they 

 are small and branched, and each has an axis-cylinder 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 

 connection with the edge of the grey matter externally, where it 

 is considerably 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 



Fig. 452. Section of spinal cord (cervical region), 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 grey matter. 7, 10, o, and 3 are tracts of descending degeneration; 

 i, 2, 4, 6, and 8, of ascending degeneration. Semidiagrammatic. (After Sherrington.) 



the grey matter of the posterior cornu ; this is known as the 

 posterior reticular formation. 



The other groups of cells (not represented in fig. 452) are 

 confined to the thoracic region of the cord, and are two in num- 

 ber, viz. : one situated at the base of the posterior cornu, formed 

 of large fusiform cells, constitutes the posterior vesicular column 

 of Lockhart Clarke (fig. 456, c c), and the other situated on the 

 outer portion of the grey matter, about midway between the 

 anterior and posterior cornua, constitutes the cells of the inter- 

 media-lateral tract (fig. 456, i T). These cells are small and 

 spindle-shaped, and are found in the upper lumbar as well as in 

 the thoracic region. 



Columns and tracts in the white matter of the spinal cord. In 



