PROFESSOR HUXLEY OX THE OSTEOLOGY OE THE GENUS GLYPTODON. 51 
The external surface of the perpendicular ramus of the mandible is rugose, slightly 
convex from above downwards and from side to side, while its internal surface exhibits 
a corresponding concavity, which is exaggerated below by the inward projection of the 
posterior alveoli, and is divided by an elevation of its surface, which ascends obliquely 
from the alveolar margin towards the coronoid process, into an anterior and a posterior 
moiety. The apex of the coronoid process is broken away upon each side, but it seems 
not to have extended beyond the level of the articular condyle, from which it is sepa- 
rated by only a shallow notch. 
The hinder margin of the perpendicular ramus, which is very thin inferiorly, thickens 
•with the rest of the bone superiorly, and ends above in a transversely elongated condyle, 
which projects further upon the inner than on the outer side of the plane of the ramus 
(Plate V. fig. 2°). Viewed laterally, this condyle has the form of a wedge, the base 
of which is O’ 7 inch broad; its hinder face being slightly concave, while its anterior 
face, convex from above downwards, and slightly concave from side to side, looks 
forwards and upwards (Plate V. fig. 2). It is this face which bears the surface for 
articulation with the squamosal element of the skull, and is indeed coextensive there- 
with. The surface in question is 1*25 inch wide from side to side, and 06 inch broad 
or from above downwards, and is tolerably smooth, but not very different from the 
adjacent parts of the condyloid process. 
The remains of five successive anterior teeth are observable in the alveoli of the left 
ramus of the mandible, and the socket of the sixth is clearly defined. Behind it, for a 
space of 1'8 inch, the inner wall of the ramus is broken away so completely that no trace 
of any alveolus is left. On the right side, the bone is nearly in the same state, but at .a 
distance of 7'6 inches from the anterior edge of the most anterior alveolus, I observe a 
smooth vertically grooved surface of bone, which is situated nearly in the same plane as 
the outer walls of the other alveoli, and which I conceive to be part of the outer wall of 
the last alveolus. 
The teeth of the mandible present the same trilobed form and other general charac- 
ters of those of the maxilla, but very few are in a sufficiently entire state to furnish 
materials for description. The first and second, on the left side, and the third, upon the 
right side, however, have their grinding-surfaces entire, or nearly so (Plate VI. fig. 5). 
The grinding-surface of the first tooth (left side) is 085 inch long and 04 inch wide 
at- widest. It has a very different form from the first tooth of the maxilla, the two 
posterior ridges of the outer surface being much more developed. 
The grinding-surface of the second tooth (left side) measures 09 inch by 045 inch; 
its outer ridges and grooves are also the better marked. The posterior surface of the 
tooth is fiat or a little concave, and its plane is directed obliquely outwards and back- 
wards. 
The grinding-surface of the third tooth (right side) is l - 05 long, and the isthmuses 
which unite its prisms are much narrower than in the second tooth. Both the anterior 
and the posterior faces of the tooth are curved. The grinding-faces of all these teeth 
