scott: toxodonta of the santa cruz beds. i 4 i 
The mandible is large and heavy. The ascending ramus is high and 
rather broad, with regularly curved and rounded angle, the free border oi 
which is not thickened, as it is in the rhinoceroses, nor yet especially thin, 
as it is in the tapirs, and is quite flat on both sides. The condyle is ses- 
sile, broad transversely, narrow antero-posteriorly and convex in both 
directions ; on the posterior face of the internal half is a well-defined ar- 
ticular surface for the postglenoid process and from the inner end depends 
a broad, hook-like plate of bone, a very exceptional feature, the purpose 
of which is not obvious. The sigmoid notch is shallow and the coronoid 
process quite low, but yet rises above the level of the condyle ; the mas- 
seteric fossa is very obscurely marked. On the anterior border of the 
ascending ramus the linea obliqua externa is not well defined, but the in- 
ternal one is very prominent distally and encloses a deep fossa behind m-g. 
The horizontal ramus is long, deep dorso-ventrally and stout, though 
laterally compressed. In the very young animal the two rami are sepa- 
rate, but they early become indistinguishably fused in a long, deeply con- 
cave symphysis, which extends back nearly to the middle of p x . The 
chin is narrow, rounded and inclined, rising steeply forward from the 
posterior end of the symphysis and thus very different from the flattened, 
procumbent chin of Toxodon. There are two mental foramina, one be- 
neath p T and the other under m x , while the inferior dental foramen has 
quite a low position. 
Little of the hyoid apparatus is preserved in connection with any of the 
skulls, but enough to show some very unusual features. The hyoid is 
attached to the antero-internal corner of the tympanic bulla. Flow very 
exceptional this arrangement is, may be made clear by the statement of 
Flower (’85, 144), who says, in speaking of the tympano-hyal : “it is 
always in relation to the hinder edge of the tympanic bone, generally 
more or less surrounded by it.” In Nesodon , on the contrary, a style-like 
bone is attached to the anterior edge and, in the adult, is ankylosed with it 
and seems to represent the coalesced tympano- and stylo-hyals. In one 
very young skull, with the milk-dentition still in use, a very small, cylin- 
drical tympano-hyal is firmly attached to the antero-internal corner of the 
bulla, but is so extremely short that it cannot possibly represent the 
long and prominent bone, which is unfortunately broken in all of the 
adult skulls. (See PI. XV.) In the young skull mentioned there is 
also a separate stylo-hyal, which is long, slender, laterally compressed 
