47 



Family II. TOXODONTHX^. 1 



Genus TOXODON/ Owen. 



' The characters which distinguish this genus of Professor Owen have 

 been derived by that naturalist from an imperfect skull, a few 

 fragments of the lower jaw, and some teeth, discovered by Mr. Darwin, 

 on the banks of the Sarandis, a small stream near Eio Negro, in South 

 America. These distinctive qualities are principally as follows : 



Incisors g, canine 2, molars g = 38. 



The incisors have cutting edges, and are rootless, but supplied with 

 persistent pulps ; of the upper ones, the two central are very small ; 

 the two external, very large and curved ; the lower incisors have, on the 

 contrary, the two middle large, with the others gradually diminishing 

 in size. The molars, separated from the incisors by a wide interval, are 

 rootless, curved (whence the generic name), and with an irregular 

 central pillar of ivory, incased in a layer of enamel, which wearing 

 unequally, give their surfaces an increased power of mastication. 



The skull is massive and elongated; the occipital region much 

 depressed, and sloping downwards towards the condyles ; the occipital 

 condyles in the same line of direction with the longitudinal axis of the 

 skull ; the nasal aperture large, and placed high up : the nasal bones 

 short and salient ; and the cheek bones of great size and strength. 



This animal, therefore for there is only one species, the Toxodon 

 platensis, Owen, whose remains are sufficiently known to represent the 

 genus assimimilates in many points to the animals of various other 

 but distinct groups which exist at the present time. 



To speculate even in a summary manner upon these counterpart 

 characters is instructive, and may possibly intimate, by accepting the 

 preponderating evidences, so adduced, the true nature of the form and 

 habits of a singular animal, known but by a few imperfect relics. 



It is said to resemble some of the extinct gigantic sloth-like 

 quadrupeds, by the rootless and pulp-bearing molars, and by their 

 massive construction ; but the presence of ten distinct incisors alone 

 forbids the idea that any further affinity existed between it and the 

 leaf-eating edentates, sufficient to justify the presumption that the 

 limbs were furnished at their extremities with long subungulated claws. 



In a somewhat greater degree it approaches the rodentia, the form 

 and composition of the cutting teeth, continually nourished by a pulpy 

 substance, and the absence of canines, supplying the resemblance ; but 

 the increased number of incisors, in direct variance with the typical 

 character of the rodent, and the structural dissimilarity of the skull, 

 lead to no inference that the feet were unguiculated to a similar extent, 

 or that the general form was that of any one of the " gnawers." 



1 r6$ov a bow, and oSofo a tooth. 



