v SPINAL COED AND NERVES 283 



curve (nr) shows that the sectional areas of the spinal roots also 

 increase at the two enlargements, so that there is a certain ratio 

 between the number of the root-fibres and the amount of grey 

 matter in the corresponding segments of the cord. The three last 

 curves (pc, Ic, ac) show that the white matter of the cord, 

 particularly that of the lateral and dorsal columns, gradually 

 increases in bulk from below upwards. 



The nerve-cells are not uniformly distributed in the grey 

 matter, but are collected into groups which occupy definite and 

 approximately constant positions in the different regions, in which 

 they form columns of cells. The largest ganglion cells are in the 

 ventral part of the ventral horn. They increase in number at the 

 level of exit of each ventral root, especially in the thoracic region 

 of the cord, which indicates its metameric origin. They also 



FIG. 171. Diagram to show relative and absolute size of sections of the grey matter, white 

 columns, and spinal roots at different levels of the spinal cord. (After Woroschiloff.) The 

 sections of the different roots (n.r.), grey matter (gr.), and lateral, dorsal, and ventral columns 

 (I.e., p.c., a.c.) are represented by curves, their common abscissa being intersected by ordinates, 

 each of which corresponds to a pair of spinal nerves. In the ordinates each mm. of rise above 

 the abscissa line corresponds to about 1 sq. mm. area of section. 



increase in number in the two enlargements, parallel with the 

 increased size and number of fibres of the ventral roots in 

 these parts. 



Another group of cells, distinct from the preceding, is found 

 in the lateral horn, mainly in the thoracic segments, where the 

 lateral horn appears as a distinct formation. Its cells are smaller 

 than those of the preceding group, and are generally spindle- 

 shaped, with their larger axes directed towards the apex of the 

 horn. 



The two dorsal grey horns, again, have at their base, particularly 

 in the thoracic region, a well-defined oval group of ganglion cells, 

 which are smaller than those of the ventral horn. This is the 

 so-called columna vesicularis or Clarke's column. In the cervical 

 segments and lower part of the lumbar cord it is represented by 

 the cervical nucleus and the sacral nucleus of Stilling respectively. 

 And in other parts of the spinal cord there are found the so-called 



