Zoological Sociehj. 399 



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 canal f, 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 Ht/stricidcE (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 Cavilna, 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 {Sphigguriis, Erethizon, Chatomys) 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 anteriorlv u-ithin 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 Comparee, 2nd edition) in several 

 cases ; I wU cite one of tliem : — " Dans le porcepic commun . . . . il y a dans I'aile 

 pterygoide externe deux canaux, I'un inferieure, s'ouvrant en arriere a la racine de 

 cette aile, un autre superieure, et s'ouvrant pres du temporal. C'est le premier 

 qui parait etre I'aualogue du canal vidien." That is, of the canalis ali-sphenoideus, 

 as 1 shall hereafter show that it is not the homologue of the vidian canal ; the 

 second alluded to by Cuvier is the canalis ali-sphenoideus extevnus. 



t Cuvier also observes, " Dans les lievres . . . . le canal vidien (the ali-sphe- 

 noid) n'est qu'un trou dans I'aile pterygoide externe," and his editors add, within 

 brackets, " et que Ton distingue dans I'orbite tout pres et en dehors du precedent." 

 The bole alluded to, however, from being situated quite in the depth of the ptery- 

 goid fossa, is much more like the interpterygoid canal in the IIi/.i/rk'id<e. 



