1917] Stock: Structure of the Pes in Mylodon harlani 



271 



... a moderately long, subcompressed bone, having its proximal end ob- 

 liquely truncated, and supporting a circular and nearly flat surface, below which 

 there is a rough tuberosity. A narrow vertical channel with a large perforation 

 in the middle, and with a convexity before and behind, characterizes the outer 

 side of this bone; its inner side is rough and similarly unequal: on neither side 

 is there the least trace of an articulation with an adjoining metatarsal. The 

 distal end presents a simple ovate articular convexity, with the small end upwards. 



As shown by Owen's figures, metatarsal 2 is fully twice as long 

 as the cuneiform with which it articulates. 



In Mylodon harlani the second metatarsal differs decidedly from 

 that of M. robustus in its relative length. This element, as contrasted 

 with M. robustus, is exceedingly short anteroposteriorly, often shorter, 



Figs. 3a and 36. Mylodon harlani Owen. Middle cuneiform and second meta- 

 tarsal, no. 22771, X Eancho La Brea beds. Fig. 3a, superior view; fig. 3b, 

 inner view. 



Figs. 4a and 4b. Mylodon harlani Owen. Co-ossified middle cuneiform and 

 second metatarsal, no. 22772, X %. Eancho La Brea beds. Fig. 4a, superior 

 view; fig. 4b, inner view. 



in fact, than the middle cuneiform in M. harlani. In the marked 

 shortening of metatarsal 2, the pes of the latter species may be con- 

 strued as being more advanced than that of M. robustus. It is to be 

 noted, however, that the middle cuneiform is relatively longer in 

 M. harlani than in M. robustus. 



The proximal and distal articulating surfaces of the second meta- 

 tarsal may almost meet dorsally, giving the element a triangular shape 

 in side view. In some specimens the proximal face is almost vertical 

 and the metatarsal therefore approximates a quadrilateral form. The 

 proximal articulating surface conforms in outline to the distal artic- 

 ulating surface of the cuneiform and may be convex below and slightly 



o Ibid., pis. 21 and 22. 



