303 



1486. The right os calcis of a large mammalian quadruped. It measures six 

 inches in length and five inches and a half in breadth ; presents two large 

 articular surfaces at right angles to each other upon its upper and 

 anterior part ; has a short calcaneal or posterior process, which is broad, 

 depressed and bent upwards, and a short thick obtuse process directed 

 downwards from the internal and under part of the bone. The inner 

 and upper articular surface is semicircular, nearly flat, very slightly con- 

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

 outer margin at a rather 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 placed 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 flexor 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 downwards 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 

 calcaneum 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 likewise 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 pre- 

 sent fossil. The calcaneum of the Mylodon robustus 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 sur- 

 face, but the calcaneal process is much larger and is continued more 

 directly backwards. The cuboidal facet in the Mylodon is much smaller 



