50 PEOFESSOE HUXLEY ON THE OSTEOLOGY OF THE GENUS GLYPTODON. 
while the length, measured in a straight line, from the symphysis to the angle of the 
jaw, is not more than 10 ‘75 inches. The horizontal ramus is very deep and thick, mea- 
suring about 3-25 inches vertically by 1-5 inch in thickness, while the ascending ramus 
is 3'5 inches wide by about 09 inch thick at thickest (Plate V. fig. 2). 
The anterior end of the mandible is 2*9 inches wide and abruptly truncated, ending in 
a rugose edge, nowhere more than half an inch thick, which, at its extremities, bends 
round at a right angle into the upper margins of the rami (Plate VI. fig. 5). These, 
thick and rounded, ascend somewhat towards the first alveolus, which is 2-25 inches 
distant from the anterior end of the ramus. The symphysis, 5 '7 inches long, appears 
to be formed, by the sutural union, and not by the anchylosis of the rami ; but the bone 
has been so broken that a large aperture occupies the middle of the symphysial space 
(Plate VI. figs. 4 & 5). 
The exit of the inframaxillary canal is nearly half an inch wide, and is situated If- 
inch below the upper margin of the jaw, and directly beneath the anterior boundary of 
the first alveolus. The anterior, or symphysial, contour of the mandible slopes, with a 
slight forward concavity, obliquely downwards and backwards to the level of the foramen ; 
and is then continued, almost straight, or with a slight anterior convexity, to a point 
nearly in the same vertical line as the hinder edge of the third alveolus (Plate V. fig. 2). 
The symphysial face is convex from side to side inferiorly, and gradually widens 
until, at its hinder end, its breadth amounts to 5 "5 inches. Its outer boundary is 
formed by an obtuse longitudinal convexity, which runs along the middle of the outer 
face of the horizontal ramus, and dies away, posteriorly, at the commencement of the 
ascending ramus. From this ridge, or convexity, the summit of which corresponds with 
the greatest outside breadth of the jaw, the outer surface of the ramus slopes upwards 
and inwards to its alveolar margin (Plate VI. fig. 4). The inner face of each horizontal 
ramus is slightly concave from above downwards, passing, in front, into the excavated 
upper surface of the symphysis. 
The general contour of the anterior half of the alveolar margin of the mandible is 
slightly convex upwards, in correspondence with the concavity of the opposed region of 
the maxilla (Plate V. fig. 2). The posterior half of the same margin is broken away ; 
but it may be assumed that it was concave upwards, answering to the downward con- 
vexity of the hinder part of the maxillary alveolar edge. 
The inner edges of the alveolar margins of the two rami are 2 inches apart. In the 
left ramus the series of alveoli is tolerably well preserved for 5^ inches, or to a point 
behind the anterior edge of the ascending ramus. From the character of the broken 
surface behind this point, however, it is obvious that the series of alveoli was continued 
along the inner surface of the ascending ramus, very nearly to the angle of the jaw, and 
considerably behind a line let fall perpendicularly from the articular condyle — an arrange- 
ment which, so far as I am aware, has no parallel among Mammalia (Plate VI. fig. 5). 
As the whole length of the series of mandibular alveoli is about 8 inches, it is pro- 
bable that the number of teeth was the same below as above, or eight on each side. 
