352 PATAGONIAN EXPEDITIONS! PALAEONTOLOGY. 
A peculiar feature noted by Ameghino (1894, pp. 112, 113) is the 
annular character of the vertebral epiphyses. A low round prominence 
from the centrum projects through the central perforation of the epiphysial 
ring. This structure is most typically developed in Borhycena , occurring 
less regularly in Prothylacynus. 
Parts of several ribs are preserved with No. 15,701, of which the two 
most complete specimens are figured (Pis. XLV, fig. 4; XLVI, fig. 1). 
The smaller of these, the second rib of the left side, is shorter than in 
Thylacynus, but slightly more robust and with thicker distal end. The 
larger rib (PI. XLV, fig. 4), from the cylindrical character of its shaft, 
evidently belongs near the middle of the thorax. The proximal end is 
more robust than any of the ribs in this region in Thylacynus. The shaft 
also is more cylindrical. 
Part of the sternum is preserved with the remains of both species of 
Borhycena in the collection. The presternal segment (PL XLV, fig. 5) 
differs from the corresponding element in Thylacynus in having the dis- 
tal portion of the posterior bar narrower and deeper. The mesosternal 
segments are shorter and proportionately narrower than in the recent 
genus. 
Appendicular Skeleton. The scapula (PI. XLVI, fig. 2), although 
smaller than in Thylacynus , has the neck of about the same length. The 
glenoid cavity is circular in outline and the coracoid process large, with 
the tip directed inwardly to about the same extent as in the Tasmanian 
genus. The high scapular spine divides the external surface into two 
unequal fossae, of which the anterior is the larger. Its surface is almost 
flat. The infraspinous fossa is deeply concave with elevated axillary 
border. The inferior angle is more acute than in Thylacynus. The 
scapular spine terminates in a long narrow acromion, the tip of which is 
missing. The supraspinous fossa is perforated by a large foramen. In 
Thylacymts several foramina pierce the base of the scapular spine, open- 
ing into the infraspinous fossa. These are represented by a single large 
foramen in Borhycena. In both genera a small foramen pierces the 
anterior margin of the neck near the middle of the suprascapular notch. 
The radius (PL XLV, figs. 2, 2 a) is of the same length as in Prothyla- 
cynus , but differs considerably in shape and is much less robust. The 
head is transversely flattened and elliptical in outline. The articular sur- 
face for the ulna is deeper than in Thylacynus and less confined to the 
