-Qg the osteology of HY/ExNODON. 
maNilUrie, are very long, and anteriorly are quite narrow and broadening poste- 
riorly, they reach their greatest width at Pi, behind wh.ch they are 
row strips by the palatines. The elevation of the alveolar borders makes the hard 
palate somewhat concave transversely. . . , , 
Tlie palatines are broad in front, where they unite in a semicircular suture with 
the maxillaries; behind this expansion they contract to form a long, narrow tube, 
and the two bones are suturally united for most of their length, notched only at 
their hinder extremities by the narrow, slit-like posterior nares. In H. leptocephalus 
the palatines are in contact throughout, and the canal appears to have no inferior 
opening at all. Such an extreme degree of backward shifting of the narial aperture 
is very rare among inainiiials, and is equalled only by the condition attained in the 
edentate genus Myrniecophaga. The pterygoids are but little exposed, as they are, 
to a great extent, covered up by the pterygoid processes of the alispheiioids. They 
are low, short, and curved, so as to continue the tubular shape of the palatines, and 
interiorly are separated only by the posterior nares, which are somewhat broader 
here than between the palatines. In H. leptocephahis the two pterygoids would 
apjiear to be in actual sutural contact. There are no distinct hamular processes, 
their place being indicated merely by rugosities. 
In all the American species the mandible has a long and shallow horizontal 
ramus, the lower border of which is gently and regularly curved from beneath the 
masseteric fossa to the incisive alveolus. H. cmicians and H. paucidens form par- 
tial exceptions to this st.atement; in the former species the lower border beneath 
the masseteric fossa is straight, the curvature beginning further forward, while in 
the latter the face is shorter, and the symphyseal region of the mandible more 
steeply inclined than in the other American species. In all the sjmiphysis is nar- 
row and very long, extending back to p3, and at an early period the two rami are 
firmly ankylosed in this region. The differences to be noted between the various 
species appear chiefly in the posterior part of the mandible and in the ascending 
ramus, l.i H. Imrridtu the coro.ioid process is high and pointed, slightly recurved, 
with a concave posterior border, and with the summit placed far in advance of the 
condyle (gee Leidy, No. 2, PI. IIIl; in H. cruentm the process is similar, but has a 
broader summit ; In //. paudi,ns, H. c-ucian,, and H. kptocephalm tl,e summit is 
still wider, the postenor border is straight and nearly vertical, and rises very 
to'riil The lira, seteric fessa is large and deep with beriers parallel 
sin “rh a r T, T - '‘“P. but rather 
small ve tica y. The condyle ,s much extended transversely and placed verv low 
hook, which is best developed .and descends fBrlh”t*i! 1 ^ **'‘’“*^ 
^rder of the tamns in /f.i»f„,Teasfs„ “t? ''''' 
O-annl Pora,nina. The optic foramen is placed quite far back of the orbit 
