104 INTRODUCTION. 



only of one long, slender, canon-like bone, with three pulley-like articula- 

 tions at its inferior extremity, for the first phalangal bone of each toe : 

 the middle of these articulating surfaces is the longest and narrowest. 

 This long metatarsal bone must, indeed, be regarded as consisting, ele- 

 mentarily, of three, consolidated together. In the Alactaga, however 

 (Dipus Jaculus), the two outer toes have each its own metatarsal 

 bone, but very slender, and only extending up each side of the middle 

 metatarsal bone for about one-third of its length. 



The metatarsal bones in the Bat are short and slender ; while, on the 

 contrary, the metacarpal bones (excepting that of the thumb), are, as 

 before stated, extremely elongated. 



Of the arrangement and number of the toes in different groups of 

 Mammalia, and of the forms and modifications of the nails, or claws, 

 which sheath the last, or ungueal phalanx, nothing need here be said ; as, 

 this topic, and, indeed, the peculiar characters of the feet, both anterior 

 and posterior, will be enlarged on in the treatment of each group re- 

 spectively. The delineation of a broad outline will be, in the first place, 

 sufficient, and the filling up will be a progressive work, as the orders, 

 families, and genera, into which the Mammalia resolve themselves, come, 

 in turn, under especial consideration ; and, if more attention has been 

 hitherto bestowed on the human skeleton than on the osseous framework 

 of the lower orders, it is because a clear knowledge of the parts of 

 which that consists, and of their mutual arrangement, is essential to an 

 appreciation of the differences and modifications traceable throughout the 

 class. 



ON THE TEETH OF MAMMALIA. 



IT is only within the last few years, that the importance of the dental 

 system of Mammalia, as being intimately connected with their economy, 

 and, consequently, with their systematic arrangement, has been clearly 

 perceived and acknowledged. From Aristotle to Ray, although the 

 form, differences, and relative position of the teeth were not altogether 

 unnoticed, no definite attempts were made to deduce, from their 

 characters, those general rules, now received and appreciated by the 

 naturalist ; or to systematize the facts presented by them, with a view to 

 the establishment of great natural groups, or orders, the first step in the 

 true science of zoology. It is unquestionable, indeed, that Aristotle 

 indicated three kinds of teeth : namely, front teeth, projecting teeth 

 (canines), and back teeth ; the latter being either flat, or, as in the 

 Gats and other Garni vora, saw- like, when regarded all together ; and he, 

 moreover, remarked, that, in ruminating animals, the front teeth, or 



