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 neurre 

 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 Pha'anger, 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 scapula; 

 and clavicles fitted to support the wings, and to 



