CHAPTER XVIII. 



THE SKELETON OF THE WILD DUCK (Anas 

 boschas). 



I. EXOSKELETOK 



The exoskeleton of the Duck and indeed of all birds is 

 entirely epidermal in origin. Its most important part consists 

 of feathers, but it includes also the following horny struc- 

 tures : 



(a) scales, which cover the toes and tarso-metatarsus ; 



(b) claws, which are attached to the distal phalanges of 

 the toes and of the pollex ; 



(c) the wide beak, which sheaths both upper and lower 

 jaws, and whose edges are raised into lamellae, which act as 

 strainers. 



FEATHERS. 



A well developed feather, such as one of the large 

 quill feathers of the wing or tail, consists of the following 

 parts : A main stem, the scapus, which forms the axis 

 running along the whole length of the feather, and is divided 

 into (1) a proximal hollow cylindrical portion, the calamus or 

 quill, and (2) a distal solid portion, the rachis or shaft, which 

 is square in section, flexible and grooved along its ventral 

 surface, and bears a number of lateral processes, the barbs. 

 The calamus which is partly imbedded in a pit in the dermis, 



