BIRDS. 
298 
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 on 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 through a pulley over the head of the scapula 
DIAGRAM OF A BIRD, TO ILLUSTRATE THE ARRANGEMENT OF THE PLUMAGE, ETC . 1 
and metacoracoid, and then being 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 gland, which is most developed 
in aquatic birds, may be absent, and when present may be either naked or crowned 
with a tuft of feathers. 
1 For this cut the Editor is indebted to Mr. Rowland Ward, in whose Sportsman's Handbook it originally 
appeared. 
