296 PATAGONIAN EXPEDITIONS: PALAEONTOLOGY. 
has a very short neck and a short trochlea, which is but little or hardly at 
all grooved, and the calcaneum has a short, heavy tuber. In the Entel- 
onychia the astragalus has a very elongate trochlea, with parallel sides, a 
long neck and very convex head, and the tuber calcis is long, laterally com- 
pressed and with much thickened free end. The Typotheria have a more 
deeply grooved astragalus, which is quite different in shape from that of 
either of the other suborders and the same is true of the calcaneum, as is 
made clear by a comparison of the plates in this volume. 
It is in the metapodials and phalanges that the most striking differences 
between the three groups of the order are to be noted. All of the known 
Toxodonta are tridactyl and the feet have a mesaxonic symmetry, which, 
however, is not perfect, and a vestigial fifth metacarpal is retained in all of 
the genera, even the latest, but no trace remains of the fifth digit in the 
pes. The phalanges are short and heavy and the unguals are broad and 
hoof-like, changing their proportions with the bulk of the animal. In 
general appearance, the feet of the Santa Cruz genera bear a decided 
resemblance to those of Eocene perissodactyls, but they are remarkably 
small and weak in proportion to the size of the skeleton. In the Typo- 
theria the number of digits is more variable ; the formula is usually IV— 
IV, but in one series, including the Pampean Typotherium , the pollex is 
retained. The symmetry of the digits is not very strongly marked and may 
be either mesaxonic or paraxonic. The phalanges are slender and elongate, 
the unguals narrow and pointed, nail-like, rather than hoof-like, except in 
the comparatively large Typotherium , in which they are short and wide. 
The Entelonychia have the most curious and aberrant type of feet, which 
in some measure resemble those of the Ancylopoda of the northern hemi- 
sphere, though it should be noted that these parts are not fully known in 
any of the genera and only approximately so in a single genus, Homalo- 
dontotherium. There are five fully developed and functional metacarpals, 
which are very long and slender ; me. V is much the stoutest and per- 
haps the longest of the series ; the distal trochleae are very unusual in 
form and indicate a remarkable degree of mobility on the part of the 
phalanges. The unguals are large heavy claws, cleft at the free ends. 
The pes is likewise pentadactyl and isodactyl in symmetry, and the meta- 
tarsals are extremely short, hardly more than one-third as long as the 
metacarpals ; mt. V is the heaviest and from the fibular border, near the 
proximal end, is given off a large process, much like that seen in the 
Santa Cruz Gravigrada. The phalanges of the pes are unknown. 
