65 
suggested, though I am not aware that he has published, the name 
of interpterygoid canal, is a characteristic of this family. There is 
another remarkable canal which exists in I think I may say the 
greater number of the species in this order, and which I have not as 
yet noticed in any species of other orders: its posterior opening is 
near the foramen ovale, sometimes on the outside and sometimes on 
the inside of the cranium; it extends forwards a short and variable 
distance, then opens externally, and serves to transmit a nerve to 
the masticatory muscles: this canal, which is not unfrequently 
double, I will here, for convenience of reference, designate the ex- 
ternal ali-sphenoid canal*. 
The Hares present characters differing from the rest of the order, 
in the absence of the ali-sphenoid canalt, and in having a distinct 
canalis caroticus excavated in the tympanic bone; the external ali- 
sphenoid canal usually exists, and is double, but from imperfection 
of bony development is not always very clearly demonstrable. 
The ali-sphenoid canal must be said to be of constant existence in 
the Hystricide (as defined by Mr. Waterhouse), although, as I before 
observed, it often coalesces with the interpterygoid, through non- 
ossification of the lamina which separates them ; for its outer wall is 
always distinct ; and even in the Caviine subfamily, where the max- 
illary bone extends back to meet the temporal, the ali-sphenoid bone 
always lines the bridge thus formed, so that the canal no less deserves 
the name which I have ventured to propose for it. The external 
ali-sphenoid canal also exists in this family ; it is not usually demon- 
strable in the Caviina, having apparently coalesced with the true 
ali-sphenoid; but in a large skull of the Capybara contained in 
the Society’s collection it is very distinctly separated. In some of 
the Hystricine subfamily (Sphiggurus, Erethizon, Chetomys) this 
canal is double, and in such of them as have the true ali-sphenoid 
canal coalesced with the interpterygoid, the lower division of the ex- 
ternal ali-sphenoid might perhaps be mistaken for it; but the true 
ali-sphenoid canal always opens anteriorly within the lamina which 
forms the external pterygoid process and the outer boundary of the 
coalesced foramina spheno-orbitarium and rotundum, while both 
divisions of the external ali-sphenoid canal open on the outside of 
this lamina ; in those species however which have the true ali-sphenoid 
canal separate, the homology is at once apparent. 
Although the arrangement of foramina in the common Rat and 
* This canal is alluded to by Cuvier (Anatomie Comparée, 2nd edition) in several 
cases ; I will cite one of them :—‘“ Dans le porcépic commun. . . . il y a dans I’aile 
pterygoide externe deux canaux, ]’un inférieure, s’ouvrant en arriére a la racine de 
cette aile, un autre supérieure, et s’ouvrant prés du temporal. C’est le premier 
qui parait étre l’analogue du canal vidien.” That is, of the canalis ali-sphenoideus, 
as I shall hereafter show that it is not the homologue of the vidian canal; the 
second alluded to by Cuvier is the canalis ali-sphenoideus externus. 
+ Cuvier also observes, “ Dans les liévres.... le canal vidien (the ali-sphe- 
noid) n’est qu’un trou dans l’aile pterygoide externe,” and his editors add, within 
brackets, ‘“‘ et que l’on distingue dans |’orbite tout prés et en dehors du précédent.’’ 
The hole alluded to, however, from being situated quite in the depth of the ptery- 
goid fossa, is much more like the interpterygoid canal in the Hystricide. 
