. Bulletin of the Department of Geology. Geology. 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
. Bulletin of the Department of Geology. Geology. 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,0 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
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