268 
PATAGONIAN EXPEDITIONS I PALAEONTOLOGY. 
The palatines extend forward to about the middle of m- as narrow, 
wedge-shaped plates ; their median contact ceases a little behind m- and 
is not carried back so far as in Adinotherium and Nesodon , so that the 
front border of the much larger posterior nares is farther forward than in 
those genera. The ventral border of that portion of the palatines which 
forms the side-walls of the posterior nares is thick and rounded, but not 
nearly so broad as in the Toxodonta, and these walls diverge more rapidly 
than in the latter and form a much wider opening. The limits of the 
pterygoids and the descending processes of the alisphenoids cannot be 
determined in either skull. 
No complete specimen of the mandible is known to me, the few which 
are to be found in the collections all lacking the ascending ramus and 
angle. It is obvious, however, from the position of the glenoid cavity 
with reference to the level of the upper teeth that the ascending ramus 
cannot have been so high as in Nesodon and that the condyle was much 
less elevated above the teeth than in that genus. Enough remains in 
one mandible to show that the linea obliqua externa is not at all promi- 
nent and the interna much more so, though far less developed than in 
Nesodon and enclosing a much shallower fossa behind m-. The hori- 
zontal ramus is of only moderate dorso-ventral depth, but very thick and 
heavy ; the ventral border is nearly straight, with but slight sinuosity, at 
least as far back as 1113. The two rami are firmly coossified in a long, 
oblique symphysis, which extends to p4 and is very deeply concave on 
the dorsal side, but the chin is abruptly rounded, rising steeply from the 
ventral border and with decidedly convex profile, which is very different 
from the gently inclined and more or less procumbent chin of most of 
the Toxodonta and Typotheria. 
As yet, nothing has been found of the hyoid apparatus, nor of its place 
or mode of attachment to the skull. 
Little is known concerning the vertebrae of Homalodontotherium. I did 
not have an opportunity to examine those in the Ameghino and La Plata 
Museum collections and neither Lydekker nor Ameghino give any descrip- 
tion of them, except of the axis, which is figured and very briefly described 
by Lydekker (’93, 45, PI. XX, fig. 5). This axis is of the same type as 
that of Nesodon and other Toxodonta, but is somewhat longer in propor- 
tion to its breadth. The centrum is much depressed and very wide 
anteriorly and the surfaces for the atlas have much the same shape as in 
