SCOTT: TOXODONTA OF THE SANTA CRUZ BEDS. 
179 
The prominent spine has no acromion and dies away gradually upon 
the neck ; there is only a remnant of the proximal metacromion about mid- 
way in the course of the spine, but no trace remains of the distal one, 
which is so very conspicuous in Nesodon. The pelvis is set at a more 
obtuse angle with the vertebral column than in the latter genus and is 
relatively shorter, but very much broader. The ilium has a short 
peduncle, but an immensely expanded and everted plate, causing a 
decided resemblance to the pelvis of the elephant. 
As already noted, the fore-limb is very short and heavy ; the humerus 
is extremely massive and has a greatly developed external tuberosity. 
The fore-arm bones, which are separate, are also very stout, especially 
the ulna, which much exceeds the radius in diameter. The hind-limb is 
much longer and the femur is by far the longest of all the limb-bones 
and, with its low, massive great trochanter, the antero-posterior compres- 
sion and flattening of the shaft and the suppression of the third trochanter, 
has considerable resemblance to that of the elephants. The leg-bones are 
ankylosed in the same exceptional manner as those of Nesodon , that is, 
fused at the proximal, but not at the distal end. They are relatively much 
shorter and far heavier than in Nesodon , but have a similar laterally 
compressed shape. 
The tridactyl feet resemble those of the Santa Cruz genus in structure 
and in the mutual relations of the various elements, but the metapodials 
are remarkably short and extremely stout and tend to an isodactyl ar- 
rangement, in which the three metapodials of each foot are of nearly 
equal weight. The phalanges also are very short, broad and thick. 
The altogether exceptional character of the calcaneo-cuboid articulation 
gives a peculiar position to the calcaneum and modifies the appearance 
of the pes, when seen from the side. 
Systematic Position of Nesodon. — That Nesodon is nearly related to 
Toxodon, and should be referred to the same suborder, is obvious from 
the most superficial comparison, but the exact relationship between the 
two genera offers a much more difficult problem. This problem can 
receive a definitive solution only when the ancestry of Toxodon can be 
traced back step by step to Santa Cruz times, for our knowledge of the 
evolutionary process is still too vague for us to determine positively the 
relation between two genera so widely separated in time and so different 
in structure. Not unnaturally, therefore, the question has been answered 
