1 64 VERTEBRATE ZOOLOGY 



The anus, the external opening of the cloaca, is a transverse 

 slit with thickened lips on the ventral surface of the trunk near 

 the base of the tail ; it will be seen when the feathers are removed. 



The tail is short and wide; it has received the name of the 

 uropygium. It is of great importance to the animal, as its long 

 quills help to support the bird in the air and to direct the course of 

 its flight. There are twelve of these tail quills in common pigeons ; 

 the number varies, however, in the different breeds. Besides these, 

 the tail bears also the tail coverts, small contour feathers at the 

 base of the quills on both the dorsal and the ventral surface. 

 The tail contains the uropygial gland, with the secretion of which 

 the bird oils its feathers ; its opening is on a large papilla on the 

 dorsal surface of the tail. This is the only skin gland in the body. 



The Appendages. Two pairs are present,— an anterior pair, 

 the wings, and a posterior pair, the legs. The wings, which are 

 homologous to the forelegs of the other vertebrates, offer an ex- 

 tensive surface to the air ; each is made up of three divisions,— 

 the proximal, middle, and distal, which correspond to the upper 

 arm, the forearm, and the wrist and hand. The hand contains 

 three digits, of which the first is free, the second and third being 

 fused together. 



The upper arm is short and partly within the trunk, and usually 

 does not bear wing quills. These are borne by the forearm and the 

 hand and are divided into two groups, the primary quills and the 

 secondary quills. The former are ten in number and are attached 

 to the hand ; the latter are about thirteen in number and are at- 

 tached to the forearm. Besides these, a small tuft of feathers, 

 which is independently movable, is present on the outer, forward 

 side of the wing. These feathers are attached to the first digit, or 

 thumb, and form what is called the ala spuria. The shorter con- 

 tour feathers on both dorsal and ventral surfaces at the base of 

 the wing quills are the wing coverts. 



The legs are each made up of three divisions,— the proximal, 

 middle, and distal,— which correspond to the thigh, the shank, 

 and the ankle and foot respectively. The thigh is within the 

 skin of the trunk and does not project beneath it. The shank 

 is the upper end of the drumstick ; it is a stout, muscular struc- 



