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 Prothylacynus 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 (PL 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. 1 ; 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, b , c) 
and Amphiproviverra (PL LIII, fig. 1). 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 (PL LIII, fig. 3 a). From this point the arteries curved 
dorsally, traversing a groove in the outer wall of the neural arch just 
anterior to the transverse process (PL 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 (PL 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. 
