166 



TEETIAEY VEETEBEATA OE THE EAYtM. 



is the larger and is widest from before backwards ; at its antero-external angle it runs up 

 on to the prominent intercondylar process (ic.p.), on the outer side of which there is a 

 deep fossa for the attachment of ligament. The outer facet (o.) is widest from side to 

 side, and beneath its outer edge there is a flattened surface, apparently for the upper end 

 of the fibula. The upper part of the not very prominent cnemial crest {en.) is divided 

 into two by a deep depression, the outer portion being the largest. The middle portion 

 of the shaft is flattened behind and convex in front ; towards the distal articulation it 

 widens out and bears on its postero-internal surface a prominence {p.) forming the outer 

 side of a groove, precisely similar to that seen in the tibia of P. headnelli. The distal 

 articulation is also like that found in the large species : there is a prominent internal 

 malleolus (i.m) bearing an astragalar facet looking outwards and forwards ; external to 



Text-fig. 57. 



Eight ulna of Palceomastodon {1) parvus: A, from front; B, from inuer side. 

 ol., olecranon process ; r.g., radial groove ; ns., radial surface. | nat. size. 



this is the main surface for the astragalus [as.), strongly concave from before backwards, 

 and is produced downwards into a blunt point both before and behind. External to this 

 surface there is a roughened facet (/.) looking downwards and outwards, apparently for 

 articulation with the fibula. The chief difference between this tibia and that of Elepltas 

 is in the form of the distal articulation. In the recent form, probably owing to the 

 increasing size and weight, the astragalar surface is much broader and more gentiv 

 concave, and this increase of width has led to the reduction of the internal malleolus to 

 a mere blunt point. Other\yise the two tibias are very similar even in small points. 



