230 REPORT — 1844. 



the bone. The inner and upper articular surface is semicircular, verj"^ slightly 

 concave, with a small part continued down or sinking from the middle of its 

 outer margin at a I'ather open angle, towards the outer or cuboidal facet : this 

 is a larger and more deeply concave surface than the preceding, with a well- 

 defined margin ; it is situated on the outer side, not anterior to the astragalar 

 surface. The astragalar surface is separated from the calcaneal and inferior 

 tuberosity by a wide and moderately deep tendinal groove, analogous to that 

 along which the tendon of the^ea;o7' longus pollicis glides in Man. The base 

 of the calcaneal process, which is united to the posterior part of the cuboidal 

 concavity, is perforated by a short canal, half an inch wide, continued down- 

 wards and forwards, and leading to a wider tendinal groove, which impresses 

 the inferior surface of the part of the bone supporting the cuboidal facet. 

 The plane of the posterior part of the calcaneal projection is at right angles 

 with the inferior rough surface of the bone. 



The characters of the present fossil calcaneum, as above briefly defined, 

 are unique. The size of the bone leads us first to compare it with the cal- 

 caneum of the Elephant or Mastodon ; but here we find two broad and flat 

 astragalar surfaces on the upper part of the bone, and a small and very 

 slightly concave surface anteriorly ; there is moreover no perforation for a 

 peroneal tendon. The same absence of such a perforation, and the different 

 proportion and relative position of the cuboidal facet, distinguish at a glance 

 the calcaneum in all the ordinary Pachyderms from the present fossil. The 

 calcaneum of the Mylodon robustiis is perforated at its outer part for the tendon 

 of the peroneus longus as it is in the present fossil ; it likewise has a stout 

 tuberosity projecting from its under surface, but the calcaneal process is much 

 larger, and is continued more directly backwards. The cuboidal facet in the 

 Mylodon is much smaller and shallower than in the present fossil, and is not 

 only placed anterior to the astragalar surface, but is continuous with it. Not 

 to dwell on the differences which the Comparative Anatomist must have im- 

 mediately perceived from the description of the present most remarkable bone 

 in the corresponding one of the Ruminantia, the Quadrumana^ the Carni- 

 vora and Rodentia, I proceed at once to state that it is only in the equipedal 

 Marsupialia, and more especially in the Koala and Wombat, that we find the 

 articular surfaces of the calcaneum two in number and of the same general 

 form, proportions and relative position as in the fossil under consideration : 

 the nearly flat internal and superior astragalar surface is, however, propor- 

 tionally narrower in the Wombat ; its outer depressed angle is shallower ; the 

 calcaneal projection is directed downwards and inwards ; the strong peroneal 

 tendon indents the outer side of the calcaneum with a groove, but does not 

 perforate the bone. The calcaneum of the Kangaroo and Potoroo has a 

 totally different form from the fossil : in these leaping Marsupialia the heel is 

 subcompressed and much elongated ; the astragalar surface is divided into 

 two small distinct parts ; the cuboidal facet is anterior, and convex vertically, 

 &c. In conclusion, it may be stated that the large fossil calcaneum here de- 

 scribed combines the essential characters of that of the Wombat with some 

 features of that of the Mylodon and Mastodon, and others which are peculiar 

 to itself: the single broad astragalar surface with its external depressed por- 

 tion coincides with the characters of the large fossil astragalus subsequently 

 to be described ; though the different form of the astragalar surface appears 

 to show the present calcaneum to have belonged to a distinct species of pachy- 

 dermoid Marsupial. 



That a large quadruped, whose nature and affinities are expressed by the 

 above epithet, formerly inhabited Australia, the characters of the present os 

 calcis would alone have rendered highly probable ; and since the same con- 



