352 



ZOOLOGY 



SECT. 



three divisions of the wing are bent upon one another in the form 

 -of a Z ; during flight they are straightened out and extended so 

 that the axis of the entire wing is at right angles to that of the 

 trunk. On the anterior or preaxial border of the limb a fold of 

 skin stretches between the upper-arm and the fore -arm ; it is the 

 alar membrane or pre-patcigium (pr. ptgrn^) A similar but much 



* 



t \U\\\\\ 



FIG. 903. Columba livia. The entire animal from the left side with most of the feathers 

 removed, ad. dy. mix. ad-digital remex ; al. sp. ala spuria ; an. anus ; au. ap. auditory 

 aperture ; cb. ring, cubital remiges ; cr. cere ; dg. 1, 2, 3, digits of manus ; dg. 1', %', 3', k' , 

 digits of pes ; hu, pt. humeral pteryla ; Ig. ligament of remiges ; ind. dg. i-mg. mid-digital 

 remiges ; net. nostril ; net. in. nictitating membrane ; o. gl. oil-gland ; pr. dg. ring, pre-digital 

 remiges ; pr. ptf/m. pre-patagium ; pt. ptgni. post-patagium ; ret. mesial rectrix of right side ; 

 ret', sacs of left rectrices ; sp. pt. spinal pteryla ; ts. mtts. tarso-metatarsus ; v. apt. ventral 

 apterium 



smaller fold extends, postaxially, between the proximal portion of 

 the upper arm and the trunk ; this is the post-patagium (pt. ptgm.). 

 In the hind-limb the short thigh is closely bound to the trunk, 

 not standing well out as in a Reptile, but directed downwards and 

 forwards ; the long shank extends from the knee downwards and 

 backwards ; and the foot is clearly divisible into a proximal portion, 

 the tarso-metatarsus (ts. mtts.\ and four digits, of which one, the 

 hallux (dg. l'\ is directed backwards, the others, the 2nd, 3rd, and 



