404 Bulletin American Museum of Natural History. [Vol. XXVII, 



A brief review of the limb structure and general skeletal characters of 

 the Mesonychids may therefore be useful at this point. 



The manus of Dromocyon (Fig. 26, B^), a Middle Eocene Mesonychid, 

 as figured by Wortman (1902) resembles in many points that of Ancodus, a 

 primitive Oligocene Anthracothere figured by Scott (1895) {cf. Fig. 26 A^). 

 The thii'd and fourth digits in Mesonyx are subequal and longer than digits 

 II and V; proximally the metacarpals overlap each other from digit II to 

 digit IV. The centrale is appressed to the scaphoid and forms the connec- 

 tion between the scaphoid and the magnum; the magnum is much smaller 

 than the lunar and articulates with metacarpals II and III, the centrale, the 

 lunar and the unciform. The scaphoid and lunar have convex surfaces 

 for the radius, the lunar is broad and rests subequally on the magnum and 

 unciform, the cuneiform is shallow and concave superiorly. The pes (Fig. 

 26, B-) is paraxonic : digits III and IV are paired and subequal and the same 

 is true of digits II and V; digit I is represented only by the entocuneiform. 

 The astragalus has a well keeled trochlea, the navicular facet is transversely 

 extended and convex antero-posteriorly, and the astragalo-cuboid contact, 

 although small, is distinct. The sustentacular facet as in Artiodactyls is 

 broadly oval. The cuboid is high, the tuber of the calcaneum long. Thus 

 in the pes every prototypal feature of the Artiodactyla is fulfilled. The 

 analogy also holds in the remaining limb bones. The humerus (Harpago- 

 lestes) has lost the entepicondylar foramen, the radio-ulnar facet is broad 

 and very Artiodactyl-like, the deltoid is a high ridge terminating in a promi- 

 nent great tuberosity, the radius is long and straight and proximally flattened 

 antl the olecranon is compressed and high. In the femur the third trochanter 

 is reduced and long, the great trochanter is prominent, the distal end is very 

 deep antero-posteriorly with very large condyles and well defined intercon- 

 dylar notch and rotular groove. The tibia and fibula suggest the Artiodactyl 

 type in the downward extension of the internal malleolar ridge, and in the 

 marked expansion of the distal end of the fibula which is closely appressed 

 to the tibia; the fibula did not however touch the calcaneum (Wortman). 

 According to Wortman the dorso-lumbars numbered 19 (D 12, L 7) in 

 Dromocyon, as in Artiodactyla (D 12-13, L 6-7). The anterior sacral 

 vertebra was expanded and alone bore the ilium as in the Artiodactyls and 

 certain other groups. The pubo-ischiadic region was relatively heavier 

 than in Perissodactyls and more as in Artiodactyls; the ilium moreover 

 was expanded as in the Oligocene Artiodactyls. 



The foregoing comparisons are by no means made with the object of 

 showing that the Mesonychida^ are ancestral to the Artiodactyla, but, taken 

 in connection with other evidence (p. 401), they appear to indicate that in 

 spite of the similarity in the carpus the Artiodactyla are widely removed 



