scott: toxodonta OF THE SANTA CRUZ beds. I 15 
bears two very prominent metacromia, given off from the spine, of which 
only the proximal one is retained and in greatly reduced form in Toxodon. 
This double metacromion does not occur in theTypotheria ; there is merely 
a small, well-defined process near the distal end of the spine. 
The clavicle, which is retained in some at least of the Typotheria (see 
p. 91), has not been found in any member of the present suborder, yet it is 
not at all unlikely that it may have persisted as late as Santa Cruz times, 
as is suggested by the prominent acromion. The unexpected discovery 
of a vestigial clavicle in an artiodactyl of the upper Oligocene (Scott, ’94, 
136) shows that only a rare and fortunate accident could bring to light so 
small and loosely attached an element. 
The pelvis is quite different from that of the Typotheria, in which the 
ilium is elongate, slender and more or less trihedral. In the Toxodonta 
the ilium has lost the trihedral form and its anterior plate is greatly ex- 
panded and everted, in a degree which varies with the size of the animal 
and reaches its maximum in the large Pampean species, in which the pelvis 
has quite an elephantine appearance. 
In the Santa Cruz genera the fore and hind limbs are of approximately 
equal length, but in the Pampean Toxodon the hind limb is much longer, 
which results in the elevation of the rump and depression of the shoulders, 
neck and head and gives a very curious appearance to the skeleton. 
The humerus is short and quite stout, becoming very massive in the 
later and larger representatives of the suborder. The fore-arm bones are 
separate in all of the known genera and the ulna remains large and heavy 
throughout the series, while the radius is relatively slender. The femur 
is the longest of the limb-bones and in the Santa Cruz genera retains a 
prominent third trochanter, which is lost in the Pampean forms, in which 
also the femoral shaft is much compressed and flattened antero-pos- 
teriorly, which gives the bone a decided resemblance to that of the ele- 
phants. In all of the known genera of the suborder the leg-bones are 
ankylosed at the proximal, but not at the distal end, a very peculiar 
arrangement ; the tibia has the shaft strongly compressed laterally, but 
has a very broad proximal end, so that the interosseous space is very wide. 
The fibula is heavy and unreduced and retains throughout the series a 
large articulation with the calcaneum. 
As already noted, the feet are curiously small in proportion to the size 
of the skeleton. Though assuredly derived from five-toed ancestors, all 
