i5 2 
PATAGONIAN EXPEDITIONS I PALAEONTOLOGY. 
height, and is strongly recurved, so that the anterior surface is convex 
and the posterior concave. Distally, it ends in a short but distinct, over- 
hanging acromion, the spine here reaching its maximum height and prom- 
inence. There are two very large metacromial processes, which project 
prominently backward from the spine. Of these the upper, proximal one 
is smaller and the lower or distal one is much longer and is expanded at 
the free end ; both are quite thin and plate-like. 
In Toxodon the scapula differs from that of Nesodon in many respects ; 
the blade is somewhat narrower in proportion to its height and the coraco- 
scapular notch is less definitely marked ; the coracoid is reduced to a 
rugose nodule, which forms no incurved hook. The widening of the blade 
above the neck is more abrupt than in the Santa Cruz genus and the cora- 
coid border is nearly straight, while the glenoid border is convexly curved. 
The spine has no acromion, but dies away gradually upon the neck, and the 
metacromion is a broad, massive, roughened area, which projects backward 
but little behind the plane of the spine and is very obscurely divided into 
two parts. It is the change in the character of the spine and its processes 
which, more than any other single feature, makes the striking difference in 
the appearance of the scapula in the two genera. 
The humerus (PI. XXIII, figs. 3-5) is short and moderately heavy. 
The head is hemispherical and sessile and projects but little behind the 
plane of the shaft ; the external tuberosity is very large, rising high above 
the level of the head, but rather narrow, not extending across the entire 
proximal end and leaving the head partially visible from the front ; the 
internal tuberosity is broken away in all of the available specimens, but, 
judging from the analogy of the nearly allied Adinotherium, it was doubt- 
less very small. The division of the bicipital groove and the development 
of the bicipital tubercle appear to have already begun, part of the bicipital 
tubercle being plainly visible in one individual. The deltoid area is a 
mere roughened line and forms no process or hook. The shaft has the 
form common to nearly all of the heavier ungulates ; the proximal portion 
is laterally compressed and very thick antero-posteriorly, while the distal 
portion is antero-posteriorly compressed and broad transversely, and the 
middle region is subcylindrical. The supinator ridge is not strongly de- 
veloped, but the external epicondyle is massive and rugose ; the internal 
one is much smaller. The supratrochlear fossa is large and well-defined, 
though not very deep, while the anconeal fossa is small and profound. In 
