no STRONG. [Vol. X. 



1 50±, about in the same transverse plane as the termination of 

 the R. mandibularis VII, and innervates the epithelium lining 

 the under side of a lateral diverticulum of the oral cavity. 



At the terminal portion of the R. mandibularis one branch 

 also proceeds dorsad and then along beneath the epithelium of 

 the labial cartilage (i7o±). It forms here a dense plexus in 

 the subepithelial connective tissue layer and apparently in close 

 apposition to the cartilage. The appearance of this plexus is 

 difficult to reproduce, but PI. VII, Figs. 5, 6, and 7, will give 

 some idea of its character. The stain is not so black as that 

 of the other nerve fibres, and the fibres of the plexus certainly 

 appear to fuse with each other, forming a true network. This 

 appearance is not so apparent in sections in which the stain is 

 less complete — or in which the plexus is more diffuse, — and 

 may possibly be due to an excessive precipitation of the silver, 

 I am not inclined, however, in view of the appearances pre- 

 sented to accept this explanation. In this plexus are numerous 

 varicosities and many free endings terminating in small knobs 

 similar to the varicosities. 



From this plexus arise at right angles innumerable twigs 

 which break up into arborisations in the epithelium surround- 

 ing the cartilage. The fibres of this plexus do not anastomose 

 but simply interlace. A good idea of their appearance is given 

 in PI. VII, Fig. 5. The thicker fibres from which they arise 

 represent the perichondral plexus mentioned above and which 

 Figs. 6 and 7 represent in horizontal section. 



It is noticeable that none of these fibres, or very few, pene- 

 trate more than about two-thirds of the thickness of the 

 epithelium. I think it is not unlikely that the explanation of 

 this lies in the character of the epithelium. The outer layers 

 of the latter consist of more flattened cells which are probably 

 partly cornified. 



It is difficult to see exactly what the significance of the 

 plexus or network closely enveloping the cartilage is. It cor- 

 responds to the basal plexuses lying in, or under, other epider- 

 mal and epithelial structures and from which the terminal fibres 

 arise. Here, however, its unusually compact character, its 

 close apposition to the cartilage and the great number of 



