128 PATAGONIAN EXPEDITIONS: PALEONTOLOGY. 



end are facets for the first pair of ribs. This is succeeded by a number 

 of mesosternal segments (how many, it is not yet definitely known) which 

 are shorter and somewhat broader, but very deep dorso-ventrally and 

 laterally compressed. Next follows the complex shown in the figure. Of 

 this, the first segment is compressed and deep anteriorly, becoming broad 

 and dorso-ventrally depressed behind. The last segment of the meso- 

 sternum is wide and flat, and somewhat constricted in front of the pos- 

 terior expansion, which bears facets for three pairs of ribs. The xiphi- 

 sternum, which, in the adult animal, is ankylosed with the last mesosternal 

 segment, is quite narrow and appears to have been short. 



The Appendictilar Skeletoti. — The scapula (PI. XIX, figs, i, id) is 

 high and rather narrow and, in its general proportions, recalls that of the 

 rhinocerotic genus Hyracodon from the North American Oligocene. The 

 position of the spine is slightly back of the median line of the blade, and 

 thus makes the prescapular fossa a little larger than the postscapular ; the 

 former has an irregular surface of low convexities and shallow concavities, 

 while the latter is more simply concave. The glenoid cavity is large and 

 concave in both dimensions and of subcircular outline, except anteriorly, 

 where the articular surface extends over upon the coracoid and is much 

 narrower. 



The coracoid is a prominent, rounded and somewhat rugose boss, which 

 is not incurved and does not overhang internally. The neck of the 

 scapula is short and wide, and there is no definite coraco-scapular notch. 

 The coracoid border is somewhat sinuous ; after a short course upward 

 and forward from the neck, it becomes nearly straight for a considerable 

 distance and curves, without angulation, into the suprascapular border. 

 The latter is quite strongly convex and joins the glenoid border by a 

 rounded angle. The glenoid border is nearly straight and inclines down- 

 ward and forward till just above the neck, where it forms a concave curve. 

 For most of its length, this border is elevated as a ridge and in the distal 

 half of its course this ridge divides into two, both ridges dying away to 

 the neck. Beginning some distance below the suprascapular border, the 

 spine rises very gently to its full height and pursues a somewhat twisted 

 course, the proximal half being deeply concave behind, and the distal half 

 more nearly perpendicular to the blade. About midway of its length, the 

 spine gives off a very large triangular, and rugose metacromion. The 

 acromion proper is also very large and round, projecting strongly back- 



