176 



ANBfAL LOCOMOTION. 



consequently to the membrane or feathers which they bear, 

 the precise angles necessary for flight. It, in fact, insures 

 that the wing, and the curtain, sail, or fringe of the wing 

 shall be screwed into and down upon the air in extension, 

 and unscrewed or withdrawn from it during flexion. The 

 wing of the bat and bird may therefore be compared to a 

 huge gimlet or auger, the axis of the gimlet representing the 

 bones of the wing ; the flanges or spiral thread of the gimlet 

 the frenum or sail (figs. 95 and 97). 



Pig. 97. 



Fig. 96. —Right wing of the Red-legged Partridge (Perdix rubra), dorsal 

 aspect. Shows extreme example of short rounded wing ; contrast with the 

 wing of the albatross (hg. 62, p. 137), which furnishes an extreme example 

 of the long ribbon-shaped wing; def, anterior margin; & a c, posterior 

 ditto, consistmg of primary (6), secondary (a), and tertiary (c) feathers, 

 with their respective coverts and subcoverts ; the whole overlapping and 

 mutually supporting each other. This wing, like the kestrel's (fig. 61, p. 

 136), was drawn from a specimen held against the light, the object being to 

 display the mutual relation of the feathers to each other, and how the 

 feathers overlap. — Original. 



Fig. 97. — Right wing of Red-legged Partridge (PercZi^c rubra), seen from be- 

 hind and from beneath, as in the beetle (fig. 93) and bat (fig. 95). The same 

 lettering and explanation does for all three. — Original. 



The Wings of Bats. 



The Bones of ths Wing of the Bat — the spiral configuration 

 of their articular surfaces. — The bones of the arm and hand 

 are especially deserving of attention. The humerus (fig. 

 17, r, p. 36) is short and powerful, and twisted upon itself 

 to the extent of something less than a quarter of a turn. 



