434 



COLLEGE ZOOLOGY 



Nostri 

 Cere 



Ear opening 

 ■Glottis 



Vas deferens 

 Ureter 



Heart 

 Crop 



Sternum 



Oil gland 



Cecum 



Rectum 



Proventriculus 



Cloaca 



Gizzard 



Pancreas 



ntestine 



Figure 306. The internal structure of a pigeon. 



The neck is long and flexible. At the pos- 

 terior end of the trunk is a projection which 

 bears the tail feathers. The two wings can 

 be folded close to the body or extended in 

 flight. The feet are covered with horny epi- 

 dermal scales, and each digit is provided 

 with a horny claw. 



Feathers 



Feathers are peculiar to birds. They arise, 

 as do the scales of reptiles, from dermal 

 papillae, with a covering of epidermis, and 

 become enveloped in a pit, the feather 

 follicle. A typical feather (Fig. 307) consists 

 of a stiff axial rod, the shaft; the proximal 



portion is hollow and semitransparent and 

 is called the quill; the flattish, distal portion 

 is called the vane. The vane is composed 

 of a series of parallel barbs, and each barb 

 bears a fringe of small processes, the bar- 

 bules, along either side. The barbules on one 

 side of the barb bear booklets which hold 

 together the adjacent barbs. The whole 

 structure is thus a pliable, but, nevertheless, 

 a resistant organ, wonderfully adapted for 

 use in flight. 



The 3 principal kinds of feathers are: 



1. The contour feathers are like that just de- 

 scribed; these have a stiff shaft and vane; 

 and since they appear on the surface, they 

 determine to a large degree the contour of 



