398 PATAGONIAN EXPEDITIONS 1 PALAEONTOLOGY. 



elevation as in Tkylacynus, but, unlike that genus, the condylar surfaces 

 are wider internally than externally. The angle is broad and strongly 

 inflected. The rami are unfused at the symphysis, which extends as far 

 back as the anterior border of the posterior premolar. Four or five men- 

 tal foramina are present, varying in number and position on opposite 

 halves of the same mandible. The most anterior and also the largest of 

 these is situated beneath the anterior premolar. 



Cervical Vertebra. The atlas and third cervical are associated with 

 the skull and feet of a specimen of A. mansaniana (No. 15,154). The 

 atlanteal intercentrum (PL LIII, figs, i, \d] is separately ossified and un- 

 fused with the neural arch. The canal for the vertebral artery pierces the 

 inner surface of the neural arch above the condyles. A smaller foramen, 

 possibly transmitting a recurrent branch of the same artery, penetrates the 

 upper surface of the base of the transverse process near its posterior edge. 

 The artery emerges on the lower surface of the atlas at the base of the 

 transverse process. The neuro-arterial canal is large and widely sepa- 

 rated from the upper margin of the cotyles by a broad bar of bone. The 

 extremities of the transverse processes are lobate, and the upper surface 

 of each is reenforced by a broad median rib. 



The neural spine of the third cervical (PL LIX, fig. 5) is proportionately 

 larger than in Thy lacy mis. The centrum is strongly keeled inferiorly, 

 and the posterior bar of the costal process supports a small diapophysis. 



Appendicular Skeleton. The humerus of A. mansaniana (PL LX, 

 fig. 4) is without internal epicondylar foramen. The supinator ridge is 

 low and does not terminate proximally in a hook-shaped process. The 

 deltoid crest is sharper than in Cladosictis or Protkytacynus. 



With the exception of the magnum, the carpus of No. 15,154 is want- 

 ing. The magnum resembles that of Borhycena in shape and in the 

 arrangement of the facets. The metacarpals (PL LIV, fig. 5) interlock 

 proximally to about the same extent as in Sarcophilus. The third and 

 fourth are equal in length. The proximal articular surfaces are convex 

 in dorso-palmar section and concave transversely. The proximal sur- 

 face of the fourth is irregularly quadrangular in outline like that of the 

 third, instead of triangular, as in Thy lacy mis and SarcopJiilits. The dis- 

 tal ends are transversely flattened, with moderately developed keels on the 

 palmar surfaces. The metacarpal of the pollex is missing, but from the 

 size of the proximal articular surface on the first phalanx of the pollex it 



