460 



MANUAL OF ZOOLOGY 



Each digit of the foot is terminated by a claw which is also 

 a horny product of the epidermis, and the beaks are of the 

 same nature. The rest of the body, however, is covered by 

 feathers, a unique type of epidermal product found nowhere 

 outside the present class. 



rcJi 



-inf.timh 



Fig. 



274. — Columba livia. A, proximal portion of a remex. ca/, calamus; z'ttf. 

 limb, inferior umbilicus; rch, rachis; sup. utnb, superior umbilicus. B, filo- 

 plume. C, nestling-down. (C, from Bronn's TliierrcicJt.) 



A feather (Fig. 274) is an elongated structure consisting 

 of a hollow stalk, the calamus or quill (cal), and an ex- 

 panded distal portion, the vexillum or vane. At the 

 proximal end of the quill is a small aperture, the inferior 

 umbilicus {inf. umb), into which fits, in the entire bird, a 



