REPTILIA.
267
and an acromion process that almost equals it
in size, is quite peculiar to the Chelonian rep-
Fig. 178.
Scapular Apparatus of Chelys.
a, scapula ; b, acromion process ; c, coracoid bone.
tiles, nothing like it existing in any other ver¬
tebrate animals : nevertheless, the relations of
these bones, and the muscles derived from
them, prove clearly enough their identity, and
allow of strict comparison with those of other
races of vertebrata.
The pelvis is always composed of three
distinct bones on each side, which contribute,
as in quadrupeds, to the formation of the coty¬
loid cavity, viz. the ilium (fig. 179, a.), which is
Fig. 179.
Pelvis of the Turtle,
a, os ilii ; b, os pubis ; c, os iscbii.
of an elongated form, and attached by liga¬
ments to the transverse processes of the
sacral vertebrae, as well as to the neighbour¬
ing part of the eighth pair of dilated ribs :
secondly, the pubis b, and the ischium c, both
of which, expanding as they descend towards
the plastrum, terminate by joining their fellows
of the opposite side.
The cylindrical bones of the extremities
resemble those of other four-footed reptiles,
and present no peculiarity worthy of special
notice, except in a geological point of view.
In the turtles, all the bones of the carpus are
flattened, and of a squarish form. In the first
row there are two bones (fig. 180, c, d.) con-
Fig. 180.
Anterior extremity of a Turtle. (After Cuvier.')
nected with the ulna ; and in the second row
there are five smaller ones (1, 2, 3, 4, 5.), to
which are appended the five metacarpal bones.
In addition to the above, there is an interme¬
diate bone (e), situated beneath the ulnar car¬
pal bone (c), and above the second and third
bones of the last row, (2, 3.) This piece,
Cuvier thinks, corresponds with the dismem¬
bered portion of the trapezoid bone, met with
in monkeys. Lastly, there is a great crescent¬
shaped bone (/), which is adherent to the
ulnar margin of the piece which supports the
metacarpal bone of the little finger : this is the
os pisiforme, although its situation is so low
down.
Between the bone (1), which supports the
metacarpal bone of the thumb, and the ra¬
dius (a), the connexion during a long period
is effected entirely by ligaments, without any
appearance of the great scaphoido-semilunar
bone which exists in the other sub-genera,
but with age a small ossicle makes its appear¬
ance in this situation. In very large indivi¬
duals, the two antepenultimate bones of the
second row are consolidated into one.
The metacarpal bone of the thumb is