THE OSTEOLOGY OF HY.ENODON. 
504 
chamber. Their breadth varies in the different species, being least in H. horridus. 
itn vanes in Lue uincjcm- o 
greatest in H. crucians and H. leptocephalus, while H. cruentus is intermediate m 
this respect. In front of the squamosals the parietals become much broader and 
articulate with the alisphenoids. The sagittal crest is long and very thin and, 
for most of its length, high, especially toward the hinder end, where the obliquity 
of the cranial cavity leaves space for it. The postorbital constriction is at or belnnd 
the fronto-parietal suture, except in H. criicians and H. leptocephalus, \uyc\\\d\ it is 
in advance of that suture. 
The squamosal is very large, making up most of the side of the cranial wall, 
and forming with the supraoccipital the sharply compressed and prominent lamb- 
doidal crest, which the exoccipital appears not to reach. The height of the squa- 
mosal varies in the different species, being, of course, the converse of the parietal 
width, and is, therefore, greatest in H. horridus, and is least in H. crucians. The 
root of the zygomatic process is placed very low down near the base of the cranium ; 
it is heavy and massive, and projects well out from the side of the skull, but the 
anteriorly directed portion is short and remarkably light. The glenoid cavity is 
broad and concave in both directions; the postglenoid process is highest internally 
and continues as a low ridge for nearly the full width of the cavity ; the preglenoid 
ridge is but feebly indicated, and in the small species not at all. The jugal is long, 
slender, and nearly straight, not arching upward, but continuing back in the line 
of the peculiar maxillary alveolar process ; it passes beneath the zygomatic process 
of the squamosal, and extends as far back as the glenoid cavity, but external to it. 
The jugal attains its greatest vertical depth at the point where it reaches the max- 
illary, from which point it tapers anteriorly and forms a very narrow suture with 
the lachrymal. There is no postorbital process on the jugal. As a whole, the 
zygomatic arch is remarkable for its length, slenderness, and straightness, and for 
its low position on the skull, the high, compressed, and isolated posterior region of 
the maxillary forms a part of it, and thus the last upper molar appears to be im- 
planted in the zygomatic arch. The very curious physiognomy of the Hycenodon skull 
IS largely due to the peculiar character and position of this arch. In view of the 
large and powerful teeth and the profound masseteric fossa of the mandible, this 
weakness of the arches is exceptional. 
As in the creodonts generally, the lachrymal is largely expanded on the face 
in ront of and beneath the orbit. In most specimens the lachrymal bears a shal- 
low int, or depression bounded behind by the elevated orbital margin. Tlie fora- 
men IS within the orbit and single. 
cove/ lozenge-shaped bones. In most of the species they 
H. crucians and b LmhigUii mrf o^fHirs 
ence of large frontal ainuso,, the rvel«t of 
species, beins greatest in H. and H. JltZ, L7ZZ 
