THE CENTRAL NERVOUS SYSTEM. 



303 



FIG. 127. Three sections 

 of the fllum terminals : , its 

 transformation into the coccy- 

 geal nerve ; b, section higher 

 up before the giving off of the 

 last sacral filaments ; <;, its 

 commencement. 



which curve around the posterior horn, and, meeting similar 

 fibres from the posterior columns, together form the posterior 

 nerve-root. These two bundles form an arciform structure sur- 

 rounding the round extremity of the posterior horn. (See Fig. 

 127.) The gray commissure occupies one-third the diameter of 

 the cord. The central canal is large, slit- 

 like, and antero-posterior in direction. To 

 summarize then, there seems to be in the 

 filum terminale, especially its lower por- 

 tion, a preponderance of the posterior or 

 sensory part of the cord. 



About two centimetres from the end of 

 the cord nearly the same picture is pre- 

 sented. The transverse section is circular 

 and about 6 mm. in diameter. Many large 

 nerve-cells appear at the outer side of 

 the anterior cornua, mostly at their junc- 

 tion with the posterior horns. Fibres from 

 this cell-group, instead of running a direct course, curve 

 backward and inward (see Fig. 127), then run forward and 

 emerge from the anterior horns. Many oval cells appear in 

 the posterior horns, which now reach the surface of the sec- 

 tion, and the posterior roots begin to show their origin from 



the posterior columns and horns. 



In the lumbar enlargement trans- 

 verse sections have a circular shape. 

 (See Fig. 128.) The white substance 

 here predominates, and has but one 

 peculiarity, which will be noticed in 

 greater or less prominence through- 

 out the remainder of the cord. At 

 the bottom of the anterior fissure is a 

 broad band of white substance called 

 the white commissure. This is formed 

 of myelinic nerve-fibres, which pursue 

 a course from the base of the anterior 

 horn of one side, forward, across the 

 median line and downward to join the 

 anterior column of the opposite side at a lower level. (See 

 Fig. 129.) The anterior horns in the lumbar region are large 

 and square, as are also the cells contained in it. The gray 



Pro. 128. Three diagrams show- 

 ing the relations of gray and white 

 matter in different regions of the cord: 

 n. lumbar enlargement ; 6. mid-dorsal 

 region ; c, cervical enlargement. 



