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