Cope.l 40^ [April 15, 



JSote on tM Structure of the Posterior Foot of Toxodon. By E. D. Cope. 



The position of the genus Toxodon in the system of Mammalia, is a ques- 

 tion upon whicli few authorities have expressed positive opinions, and 

 which is generally regarded as still an open question. In the lack of cer- 

 tainty on the subject, a separate order, the " Toxodontia," has been pro- 

 posed for its reception. It is known that the genus is ungulate, but 

 the opinions of authors are much divided as to its relations to the three 

 principal orders included under that head. Resemblances to the Probos- 

 cidea have been detected, but Professor Gervais (Comptes Rendus, 1878), 

 asserts that there is a close resemblance to the genus Hippopotamus in the 

 structure of the posterior foot. 



Having come into possession of remains of Toxodon, which include the 

 greater part of the skeleton, I make a few observations on the affinities 

 suggested by the posterior foot, the oi\\j portion just now accessible in my 

 collection. The calcaueum and astragalus have been more or less imper- 

 fectly figured by De Blainville and Burmeister, but no one has, to m}^ 

 knowledge, represented the entire foot. The calcaneum is rather short and 

 stout, and its external convex tviberosity is of unusual size. Its articular 

 surface is divided into two subequal parts, the internal of which sup- 

 ports the astragalus, the external the fibula. Thus the fibular articulation 

 is of unusual size. The cuboid facet is on the inferior face of the ex- 

 tremity of the calcaneum, thus looking directly downwards when the bone 

 is prone. In order to articulate with the remainder of the foot, the calcaneum 

 must have been inclined upwards and forwards at an angle of 45°, and the 

 cuboid inclined downwards and forwards at a similar angle. That the axis 

 of the astragalus had the latter inclination is proven by the fact that the 

 superior plane of the sustentaculum lies at that angle to the axis of the re- 

 mainder of the calcaneum. The great convexity of the external tuberosity 

 for the astragalus will also permit of such a position for the astralagus. 

 The navicular facet of the astragalus is plane and truncates the bone 

 somewhat inferiorly as well as distally, so as to present in the same 

 way as the cuboid. There is probably no cuboid facet. I have 

 not seen the cuneiform bones. The metatarsals and phalanges are robust 

 and rather short. The distal keels of the former are posterior and rudi- 

 mental. Their proximal extremities have a small lateral tarsal facet as 

 well as the principal one. The median digits are of unequal length, and 

 the lateral ones are much shorter, but robust. Whether there are four or 

 five digits I cannot definitely ascertain. 



The above characteristics are very significant. They at once refute any 

 supposition of affinity to the Artiodactyla, whether suilline or ruminant. 

 The form of the astragalus and wide fibular condyle of the calcaneum, 

 opposes the reference of the genus to the Perissodaetyla. On the other 

 hand, all the characters of the feet thus far adduced, are found in the Pro- 

 boscidea. They are not only those of that order, but they are carried to a 

 degree of exaggeration, as though Toxodon represented a high grade of 



