SCOTT : LITOPTERNA OF THE SANTA CRUZ BEDS. 29 



Like the manus (PI. V, figs. 2, 2a), the pes has a striking, but essentially 

 superficial resemblance to that of the horses, the tarsus being even more 

 radically different ft-om the perissodactyl type than is the carpus. 



The astragalus is more artiodactyl than perissodactyl in character, though 

 sufficiently unlike the former group ; it is narrow and elongate and has a 

 deeply grooved trochlea, which is slightly asymmetrical, owing to the 

 somewhat larger size of the external condyle : the neck is long, especially 

 on the tibial side, ending in quite a broad, depressed and convex head for 

 the navicular, but there is no contact with the cuboid, which is widely 

 removed from the astragalus. The external calcaneal facet is large and 

 so oblique as to have a lateral rather than a plantar presentation ; the sus- 

 tentacular facet has quite an artiodactyl appearance, being long and gently 

 convex proximo-distally, and becoming confluent with the navicular facet, 

 but is not of uniform width, broadening regularly to the distal end : a small 

 third facet for the calcaneum is on the outer side of the head. The navic- 

 ular facet is broad and convex, and, toward the fibular side, is reflected well 

 over upon the dorsal side of the neck, so that the proximal border of 

 the facet descends steeply from the fibular to the tibial side. 



The calcaneum is long and is remarkable for the elongation of the portion 

 distal to the fibular facet: the tuber is much compressed laterally, thick 

 planto-dorsally, and has nearly parallel borders ; the free end is thick and 

 rugose, but has no tendinal sulcus, such as occurs in the Artiodactyla ; the 

 fibular facet is narrow, but quite elongate proximo-distally, and is made 

 up of a posterior convexity and an anterior concavity ; the external astra- 

 galar facet is large, convex and oblique, presenting inward more than 

 dorsally. The sustentaculum is prominent and thick and its articular 

 surface is continued for some distance upon the body of the calcaneum, 

 extending to the third astragalar facet. On the tibial side, below the last 

 named facet, is an articular surface for the navicular. As already observed, 

 the distal portion of the calcaneum is very long and laterally compressed, 

 and together with the prominent fibular facet, gives a somewhat artio- 

 dactyl appearance to the bone ; the cuboid facet is deeply concave planto- 

 dorsally and oblique transversely, descending steeply toward the fibular side. 

 The navicular is broad and also relatively elongate proximo-distally, 

 strikingly so as compared with the flattened, disc-like navicular of the horse : 

 from the plantar face is given off a very long and heavy hook-like process : 

 the astragalar facet is slightly concave transversely, deeply so in the dorso- 



