r,08. THE OSTEOLOGY OF HY/ENODON. 
III. THE VERTEBRAL COLUMN. 
The atlas is short and broad ; the anterior cotyles for the occipital condyles are 
very deep extending lar back into tlie cavity of the neural canal, but they are not 
so strongly concave as in many of the recent carnivores. The neural arch curves 
upward very decidedly, giving relatively great vertical diameter to the bone; its 
antero-posterior breadth is rather small, but its thickness is unusually great. This 
arch has a nearly smooth dorsal surface, without ridges or any trace of a neural 
spine, but perforated by foramina for the first pair of spinal nerves. The inferior 
arch of the atlas is narrow from before backward, hardly more than half as wide 
as the superior; it curves downward as strongly as the neural arch does upward 
and thus the opening of the atlas is nearly circular. A rudimentary, backwardly 
directed spine represents the hypapophysis. The posterior cotyles for the axis are 
large and transversely curved, the two together describing nearly a semicircle. The 
transverse processes are straight and not very largely developed, especially from 
before backward, though they give great width to the bone. The vertebrarterial 
canal perforates the hinder edge of the transverse process, and after a short course 
opens into a depression on the ventral side. (In my former paper it was incor- 
rectly stated that this canal was not present.) The forward extension of the trans- 
verse process converts the atlanteo-diapophysial notch into a foramen. The pro- 
cesses project outward with hardly any recurvature, and this fact gives to the atlas 
its characteristic shape, quite diflerent from that found in most of the carnivores. 
The axis is a rather remarkable bone. Its centrum is of only moderate length, 
but broad and very much depressed, with distinct ventral keel ending in a hypapo- 
pliysial tubercle behind. The dorsal surface of the centrum, forming the lloor of 
the neural canal, also bears a strong median ridge. The atlanteal facets are low 
and wide, of oval shape, and with convex surfaces. Like the corresponding facets 
of the atlas, the outlines of the two together describe nearly a semicircle, very much 
as in the badger {Meles) to the axis of which, indeed, that of Hycenodon bears a 
close general resemblance. The odontoid process is very long and prominent, and 
of irregularly conical shape, tapering to a blunt point. 'The transverse processes 
are sliort compressed and slender; they are directed backward and but little out- 
ward and arc |mrforated by the relatively large vertebrarterial canals. The neural 
canal ,s higher and narrower in front, broader and lower behind. The pedicels of the 
arch are thick and heavy, but narrow antero-postcrlorlj, leaving considerable open 
EietlwH 7" r", 7 “ '“SO, tldn, 
hatchet-shaped p ate, which, though not very high, is of great fore-and-aft extent 
aygapopi.;:e^:f;fax:: 
.ow and wide, and the dorsal surface of .he ir ntdy Z 
