Februaby 1, 1894.] 



KNOWLEDGE. 



27 



perissodactyle ungulates, as represented by the rhinoceros 

 and horse, and the even-toed or artiodactyle group of the 

 order, of which we have famlHar examples in the pig and 

 the deer, the toes are never more than four in number, 

 the bones of the wrist and ankle interlock or alternate, 

 and the huckle-bone has a pulley-like surface for articula- 

 tion with the large bone of the leg. Whereas, however, 

 in the former of these two groups the middle toe is larger 

 than either of the others and symmetrical in itself, in the 

 second group it is the two toes corresponding to the second 

 and third of the human limb which are larger than the 

 others, while they are also symmetrical to a line drawn 

 between them. There is likewise a well-marked difference 

 between the huckle-bones of the two groups. The fourth 

 group, represented only by the various species of hyrax — 

 the coney of Scripture — need not detain us here. 



Turning to the proper subject of our article, we com- 

 mence our notice with one of the largest of the Argentine 

 mammals, which derives its name of ToxoiUm from the 



middle one is symmetrical in itself, an observer might, at 

 first sight, be disposed to place the toxodon among the odd- 

 toed ungulates. A closer examination would, however, show 

 that while the middle toe is not markedly larger than 

 either of the others, the bones of the wrist are arranged on 

 the linear plan, while in the ankle the upper surface of the 

 huckle-bone is nearly flat, or intermediate between that of 

 the elephants and the odd-toed ungulates. Omitting 

 mention of certain other minor peculiarities in the 

 structure of the limbs, if we now turn our attention to the 

 teeth, we shall find that these also present features 

 unknown in any living ungulates. We find, for instance, 

 in the first place, that the upper jaw is furnished with two 

 pairs of permanently-growing chisel-like teeth, comparable 

 to the single pair of incisors in the rodents or gnawing 

 mammals ; these being opposed by three pairs of nearly 

 similar, although horizontally placed, lower teeth. Such 

 permanently growing incisor teeth are, however, paralleled 

 among existing ungulates in the hyrax ; but the toxodon 



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■Rf 



!■ to. 1. — M,,lclon ut the Toxoilon. About oiu'-iweiiui ii;itiir;u 



peculiarly curved or bow-like form of its long molar teeth. 

 As shown by the accompanying figure of a skeleton pre- 

 served in the La Plata Museum, this gigantic animal, 

 which rivalled the large Indian rhinoceros in size, is 

 remarkable for the peculiar lowness of the fore-quarters, 

 in consequence of which the enormous head is carried 

 much below the line of the back." Since the creature has 

 much the general appearance of a rhinoceros, as shown 

 by its relatively short and stout neck and limbs, while 

 the number of toes to each limb is three, of which the 



• This feature is, perhaps, somewhat exaggerated in the restoration. 



stands alone in the order from the circumstance that the 

 molar teeth likewise grow throughout life, instead of 

 forming roots. Here, then, we have another point of 

 resemblance in the toxodon to the rodent order. When 

 we examine the form of the grinding surface of these 

 molar teeth, there does not appear any marked resem- 

 blance to those of any existing ungulates. The link is, 

 however, furnished by certain allied forms from the older 

 Tertiary beds of Patagonia, known by the name of Ncsodon, 

 of which the first fragmentary remains were brought to 

 Europe by Darwin, in the " Beagle " ; the toxodon being 

 confined to the Pampean deposits and the underlying beds 



