810 
PEOFESSOE OWE]N' OK THE [MEOATKEEIOI. 
The outer surface of the ilium is slightly concave near the sacrum, and is then convex 
in the direction of its longest diameter, which is from within outwards; m other- 
directions it is nearly flat : its sui-face is much broken by numerous mtei-muscular 
ridges. _ • u j r 
The pubis (Plate XXXVII. 64) is very slender where it forms the anterior border of 
the ‘ foramen ovale’ ( 0 ), but expands at its extremities, and especially where it coalesces 
rvith the ischium to form the produced and pointed ‘symphysis.’ The extent of this 
symphysis is 10 inches in a straight lure. 
The pelvis, as in the Sloths and other Bruta, shows the conversion of the^ ischiadic 
notches (i) into foramina by the anchylosis of the ischia with the posterior sacral 
vertebra (s). Each ischium, 63 , as it extends from its confluence with the sacinm. 
expands into a broad smooth plate of bone, bent outward and forward, then contracting 
as it converges inward towards its fellow, to combine with, the pubic bones at the sym- 
physis. The hinder border, forming the tuberosity, 63 , is thick and ragged ; and two or 
three perforations here indicate the original line of its separation from the sacrum. The 
part of the ischium which joins the pubis on the sacral side of the foramen ovale presents 
on its inner surface the usual oblique channel leading to that foramen. 
Among the existing species of the Order Eeuta the Sloths alone resemble the Mega- 
therium in the expansion of the iliac bones, but this is much less in comparison with 
the length of the trank; the iliac expansion is relatively greater in the Megathenum 
than in the Elephant, and is associated with a much greater proportronate srze of the 
whole pelvis and of its cavity or channel. The extreme breadth of the pelws of a large 
Asiatic Elephant is 3 feet 8 inches, whilst in the Megatherium it is upwards of 5 feet. 
The pelvis which Cuyiee was led to suspect, from the defective condition of its fore 
part in the Madrid skeleton, to be naturally open anteriorly, as in the Mt/rmecojihaga 
didactyla, is closed anteriorly, as in the Sloths, by a ‘ symphysis pubrs of short extent. 
The acetabulum (Plate XXXVIL fig. 2) presents a full oval shape, uith the lower- 
margin bisected by a narrow and deep ‘Haversian’ groove, which extends, slrghtly 
expandmg and becoming more shallow, to irear the bottom of the carfty ; the outer- 
division of the lower border of the groove is most produced. The large and deep 
acetabula look downward and a little outward. One diameter of the hemispheroid 
cavity is 8 inches, the other diameter is 7 inches; it therefore presents a plane surface 
of 43-9824 square inches, which, multiplied by 15, -with the barometer at oO inches, 
gives about 660 pounds atmospheric pressure upon the hip-joirrt of the Megatherium. 
The size and strength of the ordinary processes of the pelrfs, the breadth of the 
rough labrum of the iliac bones, and the numerous and well-defined intermuscular 
crests, indicate the unusual size and vigour of the muscular masses which proceeded 
from Ihe pelvis in different dfrections to act upon the trmik and fore limbs and upon the 
hind limbs and tail. They lead to the conviction that the resistance wliich demanded 
such forces for its overcoming must have have been of a very different nature and 
degree from any that now opposes itself to the labours of the existing vegetable feeders 
