430
MOTION.
Fig. 225.
in the Hunterian Museum, weighs 120 grains,
and has membraneous expansions which mea¬
sure about five square inches, or 24 grains
weight to each square inch of wing : the area is
as great in proportion to the weight of the ani¬
mal as in many birds, and greater than in the
Stag Beetle. The wings of the Volant Lacerta
resemble in structure those of insects rather than
of birds, the ribs supplying the place of neuras
in the former, and of the osseous framework of
the anterior extremity in the latter. They have
sufficient membraneous expansion for flight,
provided the muscles which move them were
so applied, and had sufficient force to elevate
and depress them with the necessary velocity.
The Galeopithecus, or flying Cat, and the
Pteromys, or flying Phalanger, are also fur¬
nished with lateral membranes extending from
the atlantal to the sacral extremities, to both of
which they are attached, but they are incapable
of raising the animal in the air, and rather per¬
form the office of parachutes than of true organs
of progression.
The fossil remains of the Pterodactylus show
that it was organized for flight; the pha¬
langes of the ulnar finger being greatly elon¬
gated, apparently for supporting a membrane
extending along the whole ulnar aspect of the
arm and side of the body to the leg ; a me¬
chanism which enabled these animals to move
through the air like birds. The four other
fingers are free to answer the purpose of pre¬
hension, and are terminated by curved hooks
like the thumb of the Bat.
The Cheiroptera are endowed with extensive
powers of flight. The figure of the Bat pre¬
sents an outline closely resembling that of
birds, and calculated to offer the least resist¬
ance in the direction of their motion during
flight. Their anterior extremities are con¬
structed like wings, and their whole organization
is adapted for aerial progression. The weight
of the body compared to the area of their ex¬
panded wings is very small, and hence they
have the power of raising and supporting them¬
selves in the air. The osseous system is dense,
but light, the sternum carinated, the scapulse
and clavicles fitted to support the wings, and to