COMPARATIVE ANATOMY. 90 



is SO feeble that some of the earlier naturalists doubted the 

 fact of its seeing at all. 



Notice it also remarkably developed in this bat, 



(2.) I have here a skull of one of the Plantigrade Carnivora, 

 which it will be well not to pass over. 



This that I hold in my hand is the skull of a badger. 



You will notice how much blunter the molars are than in 

 those which are strictly carnivorous. 



The different species of the family differ much in the 

 number of their pre-molars ; some having 



2—2 3—3 3—3 



3—3 3—3 4—4 



They all, however, have a uniform number of molars. 



I would call your attention to the hinge arrangement of the 

 jaw. The cavity for the reception of the convex articulating 

 condyle of the lower jaw is hollowed out deeply, and in the 

 adult grows round the condyle in such a way as to clasp it, 

 and render it impossible entirely to separate the two jaws 

 without breaking away some portion of the temporal bone. 

 Dislocation of the jaw in the badger is therefore impossible. 

 This arrangement obtains in no other animal. 



To the Plantigrada belong also the Bears and the Racoons. 



(3.) The Pinnigrada, including only the Seals and the 

 Walrus, are at once distinguished from all other mammals 

 by their peculiar extremities. 



The toes of all the feet are united by an integument, where- 

 by they are converted in use and appearance almost into fins. 



In the Morses there are neither incisors nor canines in the 

 lower jaw, but two enormous canine teeth or tusks grow from 

 the upper jaw and project downwards, whose use seems to be 

 to detach from the ground the substances on which the 

 animal feeds, and to help him to lift himself up on to the 

 rocks on which he sleeps. 



We next come to the Ungulaia 



I have here specimens of skulls illustrating the Artiodadyla 

 or even-toed ungulates ; and the Perisso dadyla or odd-toed 

 ungulates. The Pig, the Sheep, and the Fawn, belong to the 

 former. This large skull, that of an Ass, or, as for all prac- 

 tical purposes we may call it that of a Horse (the distinctions 



