662 ANIMAL PHYSIOLOGY. 
In walking, quadrupeds like the horse use the limbs alter- 
nately, and in a diagonal sequence, so that the right fore-leg 
Fic. 503.—Red-throated dragon (Draco hematopogon, Gray), shows a large membranous” 
expansion (6, b) situated between anterior (d, d) and posterior extremities, and supported 
by the ribs. The dragon by this arrangement can take extensive leaps with perfect safety. 
Fie. 504.—Flying lemur (Cateonithecus volans, Shaw). Inthe flying lemur the membranous 
expansion (a, b) is more extensive than in the flying dragon. It is supported by the neck, 
back, and tail, and by the anterior and posterior extremities. The flying lemur takes 
enormous leaps ; its membranous tunic all but enabling it to fly. The bat, Phyllorhina 
alae alee (Fig 505), flies with a very slight increase of surface. The surface exposed by the 
at exceeds that displayed by many insects and birds. The anes of the bat are deeply 
concave, and so resemble the wings of beetles and heavy-bodied, short-winged birds. The 
bones of the arm (r). forearm (d), and hand (n, n, n) of the bat support the anterior or 
thick margin and the extremity of the wing, and may not inaptly be compared to the 
nervures in corresponding positions in wing of beetle (Pettigrew). 
and the left hind-leg are associated. Trotting corresponds to 
running in man, and there is the same diagonal action. There 
Fic. 505.—The bat (Phyllorhina gracilis, Peters). Here the traveling-surfaces (rde f, an nn) 
are enormously increased as compared with that of the land and water animals generally 
(Pettigrew). r,arm; d, forearm; ef, 1, hand of bat. 
‘is also a gait natural to some horses, some dogs, the camel, etc., 
termed ambling, or pacing, characterized by both legs on the 
same side working simultaneously and alike. This is perhaps 
comparable to human walking. In galloping, all four feet are 
off the ground together for a portion of the cycle, though they 
do not strike the ground again at the same moment, 
Evolution. —It is noteworthy that with almost all quadrupeds 
the gallop is the natural method for rapid propulsion. In all 
