

298 



BIRDS. 



this, there is the concentration of muscles and other organs in this region, to which 

 some allusion has been already made. Not only are the fleshy portions of the 

 muscles of the legs mainly confined to the upper regions of these limbs, but the 

 muscles which elevate the wings are actually placed cm the under instead of on 

 the upper surface of the body. In the breast of a flying bird the great superficial 

 muscle known as the pectoralis major is for the purpose of depressing the wing: 

 beneath this is, however, a second muscle — the pectoralis minor — of which the 

 function is to raise the wing-bone, or humerus. This is effected by the muscle 

 terminating in a tendon, which passes tl irough a pulley over the head of the scapula 



—Crown 



The&ian covers. 



.Breast ....l 



Secondary corerts 



Bastard, ' 



DIAGRAM OF A BIRD, TO ILLUSTRATE THE ARRANGEMENT OF THE PLUMAGE, ETC. 1 



and metacoracoid. and then hi-ing attached on the upper surface of the humerus. 

 The result of this arrangement is that the humerus is elevated when the muscle 

 contracts. 



The same tendency to the concentration of structures is exhibited by the organ 

 of voice (syrinx) of a bird being placed within the chest, where the windpipe 

 divides into the two bronchi, instead of, as in Mammals, immediately beneath the 

 lower jaw. 



An important external feature in Birds is the frequent presence of a gland 

 termed the oil-gland, on the upper surface of the rump, the function of which is to 

 secrete oil for the lubrication of the feathers. This eland, which is most developed 

 in acpiatic birds, may be absent, and when present may be either naked or crowned 

 with a tuft of feathers. 



1 For this cut the Editor i- indebted to Mr. Rowland Want, in wh ■ ■■ // a nefr '■•■■■'■ it originally 



appeared. 



