n e s s : but in all these circumstances the affinity o f the Scelidothere with the
Megathere is prominently brought into view. There is no other known quadruped
with which the Scelidothere so closely corresponds in this respect. In proceeding,
however, to compare together the thigh-bones o f these two ex tinc t quadrupeds,
several differences present themselves, which are worthy o f n o tic e : o f these the
first is the presence in the Scelidothere o f a depression for a ‘ligamentiim te r e s’ on
the back part of the head o f the femur, near its junction with the neck o f the hone :
this is shewn in the posterior view o f the femur given in PI. X X . The head itse lf
forms a pretty regular h emisp he re: the great trochanter does not rise so high as
in the Megatherium, but, relatively, it emulates it in breadth; the small trochanter
is proportionally more developed : the external contour o f the shaft o f the femur
is straighter in the Scelidothere than in the Megathere, and the shaft its e lf is less
bowed forwards at that part. The articular condyles occupy a relatively smaller
space upon the distal extremity o f the femur in the Scelidothere, and they differ
more strikingly from those o f the Megathere, in being continued one into the
other: the rotular surface, for example, which is shewn in fig. 5 . PI. X X V . is
iormed by both condyles, while in the Megatherium it is a continuation exc lusively
o f the external articular surface.
The patella, which works upon the above-mentioned surface, is a thick strong
ovate bone, with the smaller end downwards : rough and convex externally,
smooth on the internal surface, which is concave in the vertical and convex in the
transverse directions.
O f the bones o f the leg only the proximal end o f the tibia is preserved; but
this is valuable, as shewing another well-marked difference between the Scelidothere
and M eg a th er e; for whereas in the latter the fibula is anchylosed with the
tibia, this hone, in the Scelidothere, presents a smooth flat oval articular surface,
which is shewn in fig. 2. PL X X V I I . below the outer part o f the head o f the bone ;
irom the siz e and appearance o f which, I infer, that the fibula would not have
become confluent with the tibia, even in the mature and full-grown animal.
The relative length o f the fore and hind extremities cannot be precisely determined
from the present imperfect skeleton o f the Scelidothere; but there is good
evidence for believing, that the fore extremity was the shortest. Th e humerus is
shorter than the femur b y one-ninth part o f the latter bone ; and the radius,
which wants only the distal epiphysis, must have been shorter than the humerus.
Now the relative development o f the fore and hind legs is one o f
the points to be taken into consideration in an attempt to determine the habits
and nature o f an extinct mammal.
In climbing animals the prehensile power is more essentia l to the hinder than
to the fore parts or extremities. In the leech the principal sucker is in the t a i l ;
and higher organized climbers, in like manner, depend mainly on their posterior
claspers in descending trees, and hold on by means o f them whilst sele cting the
place for the next application o f those at the fore part o f the body, whether their
place be supplied by the beak, as in the Maccaws, or the fore-feet or hands in the
Mammalia.
But, although we perceive the hinder limbs to be the la st to lose the advantageous
structure o f the hand in the Quadrumanous species, and notwithstanding
that the tail is for this purpose sometimes spe cia lly organized to serve as a prehensile
instrument, y e t we find that the power o f grasping the branches o f trees
by either legs or tail is never maintained at the exp en se o f undue bulk and weight
o f those oi’gans. On the contrary, as the fore-limbs are the main instruments in
the active exertions o f climbing, so they are the strongest as well as the longest
in all the best climbers, and the weight o f the body which they have to drag along
is diminished by dwarfish proportions o f the hinder limbs, as in the Orangs and
the Sloths.
Can those huge quadrupeds have been destined to climb that had the pelvis
and hinder extremities more ponderous and bulky in proportion to the fore-parts
o f the body than in any other known ex isting or extinct vertebrate animals?
M. Lund argues for the scansorial character o f the Megalonyx, because its
anterior extremities are longer than the posterior ones ; but if they somewhat e x ceed
the hind-legs in length, how vastly inferior are they in respect o f their
breadth and thickness. The prehensile faculty o f the hinder limbs o f the best
climbers, as the S lo ths, Orangs, and Chameleons is by no means dependent on
the superior mass o f m uscle and bone which enters into their conformation, but is
associated with the very reverse conditions.
It is impossible to survey the discrepancy o f size between the femur and the
humerus o f the Scelidothere, as exhibited in PL X X ., without a conviction that it
relates to other habits than those o f climbing trees. The expanse o f the sacrum,
the evidence o f the muscular masses employed in working the hind leg s and tail,
which is afforded by the capacity o f the cavity lodging the part o f the spinal marrow
from which the nerves of those muscles were derived, both indicate the
actions o f the hind-legs and tail to have been more powerful and energetic than
would be required for mere prehension : and the association o f hinder extremities
so remarkable for their bulk, with a long and powerful tail, forbids my y ielding
assent to the speculation se t forth by M. Lund, as to the prehensile character o f
the tail of the Megalonyx.
Astragahis.—In the examination o f this characteristic bone I have kept in view
the question o f the habits o f the Megatherioid quadrupeds in general, and the
especial affinities of the Scelidotherium, in illustration o f which I shall notice at