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 portions of these limbs, but the 

 muscles which elevate the wings are actually placed on the under instead of 011 

 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 



Tfteiidn coverts 



Breast...'.'::.. _ 



Secondary coverts 1'j.j -^C 

 Ba.sla.-rd.wi 



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



and metacoracoid, and then being attached on the upper surface of the humerus ; 

 that bone being accordingly 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. Eowland Ward, in whose Sportsman's Handbook it originally 

 appeared. Acknowledgments are likewise due to the same gentleman for the copyright of the head of the Musk-ox 

 on p. 210 of Vol. IT., which is taken from a photograph of a specimen shot by Lord Lonsdale and mounted by 

 Mr. Ward. 



