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PATAGONIAN EXPEDITIONS I PALAEONTOLOGY. 
Pachyrnkhos. Very little is known concerning the vertebral column of 
the Entelonychia. 
The Limb-girdles display characteristic modifications in each of the 
three suborders. In some, if not all, of the Typotheria there is a clavicle 
and the scapula has a prominent acromion and a single large meta- 
cromion, given off from the spine near the distal end. The pelvis is 
unguiculate rather than ungulate in form, retaining the narrow, more or 
less trihedral ilium. There is very considerable change in the limb-girdles 
between the Santa Cruz and the later genera of the Toxodonta ; in the 
former the scapula has a well-defined acromion and two very prominent 
metacromia, one arising near the middle of the spine and the other near 
the distal end, while in the Pampean Toxodon there is no acromion or 
distal metacromion and the proximal one is so reduced as to be hardly 
more than a thickening of the spine. No trace of the clavicle has yet 
been found in any member of the suborder and it is highly improbable 
that the bone was present in the post-Miocene genera, but the distinct 
acromion in Nesodon and Adinotherium indicates the possible presence of 
the clavicle in more or less reduced and vestigial form. In the Santa 
Cruz genera the pelvis is not greatly modified, the iliac plate being but 
moderately expanded and very little everted, but in Toxodon the ilium 
is so broadened and flared outward as to give the pelvis quite a probos- 
cidean appearance, and the same is true, in less pronounced degree, of 
Homalodontotherium ; otherwise, nothing is known of the limb-girdles 
of the Entelonychia. 
The Limb-bones vary much, though chiefly in their proportions, accord- 
ing to the size and weight of the animal. The fibula articulates largely 
with the calcaneum in all members of the order, except a few of the Typo- 
theria, in which this articulation has been secondarily lost. In this group, 
which is made up almost entirely of small animals, the limb-bones are 
slender and weak and the processes for muscular attachment are mostly 
low and inconspicuous. The ulna and radius are always separate and the 
tibia and fibula are sometimes so, but in most of the genera they are 
coossified at both proximal and distal ends. The femur has the third 
trochanter, the humerus has an epicondylar foramen. The Santa Cruz 
Toxodonta have limb-bones very like those of the Typotheria except for 
their larger size and greater relative stoutness ; the epicondylar foramen 
is lost ; the tibia and fibula are ankylosed at the proximal end only, not 
