194 WILLIAM F. ALLEN 



Figures 25 and 26 are *more peripheral sections of the same 

 series, no. 64. They exhibit the same general arrangement of 

 the trigeminal nerve, but the various nerves are more scattered 

 and the nervus ophthalmicus does not appear in these sections. 

 In figure 25 the most peripheral of the two deep temporal nerves 

 {Tern.) will be seen leaving the N. masticatorius for the temporal 

 muscle. Also the masseter nerve (Mas.) is about to give oE 

 branches to the masseter muscle. As in the previous sections, 

 degenerated descending mesencephalic root fibers appear only 

 in the masseter, pterygoid, and deep temporal branches of the 

 N. masticatorius (Mast.). In the more peripheral section 

 (fig. 26), the buccal branch (Biic.) of the- masticator nerve has 

 left the main trunk; only the masseter and pterygoid branches 

 remain. Figure 27 shows the N. masticatorius from the same 

 section as figure 26 sufficiently magnified to permit of the accu- 

 rate drawing of every particle of degenerated myelin. Thus far, 

 the pterygoid nerve (Pter.) has not branched and contains about 

 the same number of degenerated descending mesencephalic root 

 fibers as it did in a more proximal section (fig. 24). On the 

 other hand, the masseter nerye {Mas.) has branched several 

 times and is appreciably smaller, but still maintains about the 

 same ratio of degenerated to normal fibers in the main stem and 

 its branches. In this section (fig. 27) the masseter and ptery- 

 goid nerves are about the same size, but the pterygoid has a few 

 more degenerated descending mesencephalic root fibers. 



Similar sections from the left trigeminal nerve from series 

 no. 67 could have been selected to demonstrate that the distri- 

 bution of the descending mesencephalic root fibers is confined 

 solely to the so-called purely motor branches of the N. masti- 

 catorius. In this experiment a few of the masseter muscle fibers 

 were left attached to the masseter nerve upon removing it from 

 the animal, and in section it was possible to trace degenerated 

 descending mesencephalic root fibers to' a branch of the masseter 

 ner\'e going to these muscle fibers. Also in the lower part of figure 

 30, which is from a peripheral section from series no. 65, where 

 the descending mesencephalic and many trigeminal motor root 

 fibers were severed, a branch from the masseter nerve (Mas.), 



