600 TEXTBOOK OF ZOOLOGY 



of the head. From the location, the vision is necessarily monofocal. 

 The eyeball is slightly movable and is provided with an upper lid, 

 lower lid, and a semitransparent nictitating membrane which ex- 

 tends across the eye from the inner corner. The ear is lacking in 

 external conchal cartilage, but appears below and behind the eye 

 on each side as the opening to the external auditory meatus. This 

 is usually guarded by a few stiff short feathers. On top of the 

 head is the comh and below the angles of the jaws are the wattles. 

 These are highly vascularized, fleshy modifications of the skin in these 

 regions, and are frequently different in the two sexes. 



The mobile neck is quite long and joins the dorsoanterior point of 

 the trunk. The trunk is more or less basket-shaped, with the pair of 

 wings folded at the sides. The skin stretching from the body to the 

 wing is the alar membrane. The body stands almost erect on the 

 strong legs. The distal part of the hindlimbs are devoid of feathers 

 but are covered with scales. The toes are provided with nails or 

 claws which originate in the epidermis. The dorsal surface consists 

 of a horny plate which is set in a matrix. The forelimbs and girdle 

 are modified for flight, while the hindlimbs and girdle are modified 

 for bipedal locomotion. The skin which covers the chicken is very 

 thin and does not contain sweat glands, neither does it have a gen- 

 eral distribution of oil glands. The oil is supplied by a tail gland or 

 uropygial gland. The bird squeezes a quantity of oil from this gland 

 into its beak and passes the beak over all feathers one at a time until 

 they are all preened. This treatment renders the feathers practically 

 impervious to water. 



The feathers are skin developments arising in dermal papillae 

 which are well set in the skin. There are three types of feathers : 

 contour (flight or quill) feathers with a stiff shaft and firm texture; 

 down (plume) feathers with a soft shaft and a free fluffy arrangement 

 of the barbs ; and filoplume feathers with hairlike structure consisting 

 of a slender shaft and a few or more branches. A typical feather is 

 composed of a quill which sets in the feather follicle of the papilla of 

 the skin and continues up into the feather as the shaft. The shaft 

 bears slender barbs which extend obliquely from it to make up the 

 principal surface of the feather. The barbs in turn bear still smaller 

 and more slender projections known as barbules, which hook the barbs 

 together. The barbs in normal position make up the vane, and give 

 the feather a smooth surface. At the end of the quill there is a small 



