94 THE DESEADO FORMATION OF PATAGONIA 



are slightly shorter than Me. Ill, but not materially weaker, 

 so that all three would reach the ground when the animal 

 was standing. Though closely packed, the metacarpals 

 are not grown together at any point. Distally each has 

 a narrow trochlea, which carries a median crest on the 

 palmar side only. Under the distal end of each metacarpal, 

 there is a pair of small sesamoid bones. 



All the phalanges are very short and weak, with the 

 articular surfaces cut under obliquely, suggesting that the 

 toes are bent upward. Distally each toe ends in a slender 

 cleft ungual phalanx, suggesting a claw-like hoof. Rhyn- 

 chippus clearly walked in a semidigitigrade manner, the 

 weight coming principally on the metapodials, the foot 

 as a whole resembling that of a dog. 



The pelvis is unidentified. Though the bones are of 

 about the same weight, the hind limb is longer than that 

 of Adinotherium. The femur has a rounded head on a 

 short but distinct neck, with the pit for the round ligament 

 on the posterior margin of the head. The narrow digital 

 fossa is deep. The greater trochanter is rugose and strong, 

 but does not rise quite to the height of the head. The 

 lesser trochanter makes a strong shelf-like process well 

 below the head, while the third trochanter is a prominent 

 process about the middle of the shaft, on the posterior side. 

 The shaft is broad and flattened above, but narrows and 

 becomes circular in section below. The condyles are rela- 

 tively small, the inner being the smaller and more convex, 

 while the outer is broader and less convex. 



The tibia and fibula are a little longer than the femur, 

 fused proximally, free distally, as in toxodonts. The prox- 

 imal end of the tibia is too weathered to permit detailed 

 description. However the upper end is wide and flattened 

 from front to back. Distally the bone narrows until the 

 lower part of the shaft is circular in section, the distal end 

 enlarging again in the neighborhood of the articulation. 

 The fibula has a broad facet for the inner side of the astra- 



