PROFESSOR HUXLEY ON THE OSTEOLOGY OE THE GENUS GLYPTODON. 53 
the zygomatic processes of the two specimens do not differ more than those of opposite 
sides in the same specimen. 
3. In the typical specimen the upper ends of the three anterior alveoli, on each side, 
are preserved; they occupy just the same space as the three anterior alveoli of the 
present specimen. 
4. The presphenoid in the type has the same crest, and the inner ends of the optic 
foramina are precisely the same distance apart. 
When to these correspondences we add that the distance from the front edge of the 
nasals to the level of the posterior edges of the supraorbital prominences is the same in 
both skulls, and that the lower jaw of the new specimen would fit very fairly on to the 
typical skull, it will, I think, be admitted that there is sufficient evidence of the specific 
identity of the animals to which the two skulls belonged, and that the imperfections 
of the new specimen may be supplemented by the evidence afforded by the typical 
example. 
Further data as to the Cranial Structure of Glyptodon furnished by the typical skull. 
— Professor Owen (‘ Catalogue of Fossil Mammalia and Aves,’ p. 384) thus describes 
the fragmentary skull of the typical specimen of Glyptodon clavipes : — 
“ The occipital condyle (a) presents a convexity in the vertical direction, which 
describes more than a semicircle, and is slightly convex transversely, but is narrower in 
that direction than it is in the Mylodon : it is directed in the Glyptodon backwards and 
obliquely outwards. The occipital foramen (b) is very large and transversely elliptical ; 
its plane is inclined from below upwards and backwards 20° beyond the vertical line. 
The anterior condyloid foramen (c), though large, is relatively smaller than in the Mylo- 
don, and is situated close to the anterior border of the condyle. The depression for 
the digastric muscle ( d ) is perforated and separated from the condyle by a wider tract 
of the paroccipital (e) than in the Mylodon ; and the petromastoid ( f ) below the digas- 
tric depression presents a rough convexity, bounded posteriorly by a transverse ridge of 
the paroccipital instead of the hemispherical depression for the articulation of the stylo- 
hyoid bone which characterizes the skull of the Mylodon . The basioccipital ( g) pre- 
sents a median smooth concavity and two lateral rough depressions, which are continued 
on to the basisphenoid (A), and indicate the insertion of very powerful ‘ recti-capitis 
antici majores’; the obliterated suture between the basioccipital and basisphenoid forms 
a rough transverse ridge. The inequalities of this part of the basal region of the skull 
present a striking contrast to the broad smooth and even tract which the same part 
forms in the Mylodon. The sides of the concave under surface of the basisphenoid are 
bounded by longitudinal ridges, which have been broken off in the specimen. The 
petrous bone terminates by a prismatic pointed process in the foramen lacerum (i), 
which here gives passage both to the jugular vein and internal carotid. The foramen 
ovale (k) is circular, and of the same size as the anterior condyloid foramen. The fora- 
men rotundum (l) is one inch and a half in advance of the foramen ovale, and opens 
with the commencement of a deep and long groove, which traverses the base of the 
