812 
PEOFESSOE OWEN' OE THE I^IE&ATHEEIUM. 
portion is slightly convex transversely, in which direction the extent is scarce!) 2^ inches. 
The entocondyloid surface (^) is of nearly twice that breadth ; is of a renifonn shape, 
and is convex in every direction. The intercondyloid channel is roughened by decus- 
sating ligamentous impressions and ridges, with some vascular pits. Its narrowest part 
is anterior, and measures an inch and a half across ; posteriorly it is 3 inches across. 
The intercondyloid border of the inner condyle is sharply defined and projects below 
the level of the canal, that of the outer condyle is mostly on a level mth the canal. 
The surface of the canal meets the hind surface of the femur at almost a right angle, 
the intervening ridge being rounded off. The fore part of the inner condole stops short 
of the fore part of the shaft; the back part of the condyle projects 1 inch beyond the 
back part of the shaft. The process or prominence above the inner condyle {eimnenha 
entocondyloidea, Plate XXXVIII. ic) forms an obtuse angle, the lower side of which 
is rough, rather flattened, and expands as it descends towards the articular part of the 
condvle. The outer condyle does not project so far back as the inner one . its supm- 
condyloid prominence {ec) is larger, of a similar angular form, but is bent forward as 
well as outward. 
In the Elephant, Mastodon, and Diprotodon, the shaft of the femur is flattened from 
before backward ; but the length of the femur so far exceeds its breadth, that, strong 
as the thigh-bones of these quadrupeds are and well-proportioned to the weight the) 
had to sustain, they appear weak and even slender when placed by the side of the femin 
of the Megatherium. The Ehinoceros, which has the thigh-bone relatively broader 
and flatter than in the proboscidian pachyderms, differs more markedly from the Mega- 
therium in the presence of the third trochanter. 
The shaft of the femur is more or less flattened in all the species of Bnita ; but the 
Orycteropus and Armadillos, in which this character is conspicuous, differ, like the Ehino- 
ceros, from the Megatherium in having the third trochanter. This process is not present 
in the Pangolins {Manis), Anteaters {Mynnem])1iaga) or Sloths {Bradypus) ; but in all 
these genera the femur is relatively longer and more slender than in the Megatheiiiim, 
and only the Sloths amongst existing Mammals, not marine, repeat the remarkable mega- 
therioid character of the absence of a medullary cavity in the shaft of the femur-. 
The general characters of the femur of the Megatherium are most closely repeated in 
that of the Mylodon* and Scelidotheriumf. In these genera, however, instead of the 
shallow notch, there is a deep and prolonged fossa for the liganieiitum teres on the 
middle of the hind border of the head of the bone. The post-trochanterian depression 
is relatively larger in the Mylodon, the small trochanter is relatively less and higher- 
placed ; the whole femur is longer in proportion to its breadth, arrd the distal expansion 
is relatively less. Here, also, the articular surfaces offer a well-rnar-ked character ot 
distiirctiorr ; the rotular articular surface is corrtiiruous with that of both condyles, arrd 
unites them anteriorly. 
* OwEK ‘ On the Mylodon Tohustu^,’ 4to. p. 111. pi. 17. 
f Ib. ‘Fossil Mammalia’ of tlie ‘ Voyage of the Beagle,’ 4to. pi. 25. fig. 5. 
