380 PATAGONIAN EXPEDITIONS I PALAEONTOLOGY. 



as in Thylacynus, but less steeply inclined posteriorly than in that genus. 

 The superior and posterior borders correspond in shape to the same 

 region in Prothylacynus. As a whole, the coronoid is proportionately 

 broader and higher and the masseteric fossa better defined anteriorly 

 than in Thylacynus. The lower border of the horizontal ramus lacks the 

 convexity observable in Prothylacyttus and Thylacynus. The rami are 

 united in ligamentous suture at the symphysis, which extends as far back 

 as the anterior half of the posterior premolar (PI. LIX, fig. 7 a). The 

 mental foramina vary greatly in number and position in different indi- 

 viduals of the same species and even on opposite sides of the same man- 

 dible (cf. Pis. LVI, fig. i ; LIX, fig. 7), and are of no diagnostic importance. 



Vertebral Column and Ribs. Cladosictis resembles Prothylacynus in 

 having the atlanteal intercentrum firmly fused with the base of the neural 

 arch (PI. LIII, fig. 3^). The intercentrum retains to a slight extent only 

 the posterior emargination observable in Thylacynus and Borhycena. 

 The foramina for the exit of the spinal nerves are separated from the 

 anterior atlanteal margin by a broader osseous bar than in Prothylacynus, 

 resembling rather in this respect the atlas of Thylacynus (text-fig. 5, 6, c) 

 and Amphiproviverra (PI. LIII, fig. i). The canals for the vertebral 

 artery enter the neural arch within the spinal canal on a level with and a 

 short distance anterior to the superior border of the atlanteal condyles. 

 They emerge on the lower surface of the atlas at the bases of the trans- 

 verse processes (PI. LIII, fig. 3*7). From this point the arteries curved 

 dorsally, traversing a groove in the outer wall of the neural arch just 

 anterior to the transverse process (PI. LIII, fig. 3) and entered the neuro- 

 vascular foramen. The margins of the transverse processes in the speci- 

 mens studied have not been preserved. Their antero-posterior basal 

 constriction is much less than in Thylacynus. The anterior margin of 

 the neural arch supports a pair of tubercles, separated by a deep groove. 

 In Thylacynus there is but a single median prominence in this region (cf. 

 text-fig. 5, b). 



The axis (PI. LII, fig. 4) carries a powerful, hatchet-shaped neural spine, 

 which projects anteriorly as far as the odontoid and posteriorly beyond 

 the zygapophyses. The ventral surface of the centrum is strongly keeled 

 posteriorly. On either side of the keel is a depressed area, bounded by 

 the dependent edges of the transverse processes, as in Borhycena and 

 Prothylacynus. 



