ON A QUADRUPED. 339 



too remote or too general to assure us of any direct 

 affinity, and we are to seek in the configuration of 

 the cranium of this animal chiefly for a similarity with 

 the Cavys that really exists ; 1 refer particularly 

 to the enormously dilated foramen, before the or- 

 bit of the eye, the unusual width of the zygoma- 

 tic arch, combined with the width of the frontal 

 bones, which are almost undiminished by the orbital 

 cavities, and the form and curvature of the inferior 

 jaw. This dilatation of the anterior foramen may 

 be recognised, though in a less degree, in the common 

 Gui iea pig as it is improperly called, (Ancema, F. 

 Cuvier.) But were all the characters arrayed in the 

 above comparison, far more strikingly coincident than 

 they really are, we should, nevertheless, regard them 

 as insufficient to establish a generic identity ; for '< it 

 is impossible," says Cuvier, u to find any common 

 and positive character of those animals which Linnae- 

 us and Pallas have united together under the name of 

 Cavia, excepting that of their imperfect clavicles." I 

 would, therefore, conclude, as the consequence of 

 this comparison, that Isodon forms a more intimate 

 medium of connexion than we have hitherto possess- 

 ed, between the old genera and of Mus and Cavia. 



I have been led to. make the foregoing comparisons 

 with genera already established, in order to show that 

 a reference of this animal to either of them would be 

 unnatural and injudicious in the present state of zo- 

 ological knowledge, and to convince myself and 

 ethers that if it has been assigned to any place in the 



