PEOFESSOE OWEN ON THE SCELIDOTHEEE. 
107 
The length of the lower jaw (Plate VIII. figs. 4 & 5) is I foot 6 inches 9 lines. The hori- 
zontal rami, each 3 inches 8 lines in depth at the base of the coronoid process {b\ 
decrease in that diameter, at first gradually, then more rapidly at the beginning of the^ 
symphysis {d), to its end [d'): they are confluent at the symphysis for an extent of 
6 inches 9 hues (ib. fig. 6 d, d'). The ascending ramus of the jaw, or posterior apophy- 
siary part, presents the broad, backwardly produced, slightly inflected angular process (c) 
common to all the Megatherioids ; in shape and other minor characters it most resembles 
that in the Mylodon. The condyle (a) is transversely oblong, with the inner and smaller 
end bent a httle back : the articular sm-face is nearly flat. The posterior border of the 
ramus is continued from the reflected inner angle of the condyle, the coronoid process (^) 
from the fore-part of the condyle near the thick outer end : the extent of the base of the 
coronoid process is 4 inches, the deep notch dividing its reflected apex (b) from the con- 
dyle (a) is but 7 lines wide: the fore margin of the process describes a regular con- 
vexity : the outer side of the process is flat, the inner side convex near the anterior 
border, shghtly concave elsewhere : the low ridge bounding anteriorly that concavity is 
continued into another, which runs along the middle of the inner side of the horizontal 
ramus for 2 or 3 inches. The angular process (c) is concave internally : its upper- 
border is notched, and its outer convex side is grooved for muscular attachments. The 
coronoid and angular processes are obviously the two great handles of the jaw, which, 
grasped by the opposing masses of muscles, enabled them to move with effect the lower- 
molars horizontally upon the upper ones ; the flat condyle and broad flat surface for its 
articulation offering no obstacle to those grinding movements. The dental carral com- 
mences by an obhque orifice, 6 lines in diameter, situated 2 irrches behind the last 
alveolus (^ v), and from I to inch below the level of its outlet. The canal soon bifur- 
cates, the outer branch leading to the large orifice (ib. fig. 4 g) outside and below the 
anterior part of the base of the coronoid process ; the inner division supplies the teeth, 
and then subdi\ides into two small canals which have their outlets on the outside of the 
symphysis, fr’om 2 to 4 inches distance fr-om its extremity. These ‘ mental foramina ’ 
{h, h) are small in comparisorr -with those in the Mylodon. The horizontal ramus is 
moderately convex below and tumid externally at the molar region. 
The series of fom- alveoli in each ramus measm-es 4 inches 3 lines. The outer alveolar 
wall describes a slight curve, convex oirtwards ; it is higher than the inner one, and forms 
a kind of ‘ bead ’ or rounded prominent border externally : the whole alveolar part of 
the ramus inclines inwards. The inner alveolar wall is thin, straight, nearly parallel 
with that of the opposite side ; but a little divergent anteriorly, where it blends with the 
outer wall to form the obtuse upper and outer border of the long symphysial part of the 
jaw. This part, near 7 inches in length, deeply excavated behind, becomes gradually 
shallower to the end, which is cut square off, and is slightly notched in the middle. 
There is a slight median prominence on the under part of the symphysis near the anterior 
end. 
The teeth of the Scelidothere, as in the other known gravigrade Sloths, are eighteen 
