TOPOGEAPHY OF THE BODY. 15 



rest with st;il)ility on the water; a duck or a diver shows this well. Speak- 

 ing of shape of body, I must allude to the 



§ 34. Centre op Geavity of a bird, and show the admirable provision 

 by which this is kept beneath the centre of the body. The enormous breast- 

 muscles of a bird are its heaviest parts; sometimes they weigh, to speak 

 roundly, as much as one-sixth of the whole bird. Now these are they that 

 effect all the movements of the wings at the shoulder-joint, lifting as well as 

 lowering the \vings ; did they all pull straight, the lifters would have to be 

 above the shoulder; but they all lie below, and the lifters accomplish their 

 oiEce by running through a pulley, which changes their line of traction ; they 

 work, in short, like men hoisting sails from tlie deck of a vessel ; and thus, 

 like a ship's cargo, a bird's chief weight is kept below the centre of motion. 

 Topheaviness is further obviated by the fact that birds with a long, heavy 

 neck and head draw this in upon the breast, and extend the legs behhid, as is 

 well shown in a heron flying. The nice adjustment of Ijalance by the vari- 

 able extension of the head and legs is exactly like that produced by shifting 

 the weight along the bar of a steel-j^ard ; this, with the slinging of the chief 

 weight under the wino-g instead of over or even between them, enables a 

 bird to keep right side up in flight, without exertion. 



Sub-sect. 1. Of the Body ; its Tojoogrcqihy , etc. 



§ 35. Besides being divided as above into body and members, the exte- 

 rior of a bird is further subdivided ; the body being mapped out, mainly for 

 purposes of description, into regions, and the members being similarly re- 

 solved into their component parts or organs. We have first to notice, as 

 the most general, the 



§ 36. Upper and Under Parts. Draw a line from the corner of the 

 mouth along the side of the neck to and through the shoulder-joint and 

 thence along the side of the body to the root of the tail; all above this line, 

 including upper surface of wings and tail, are upper jJCirts ; all below, includ- 

 ing under surfaces of wings and tail, are under parts; called respectively, 

 "above" and "below." The distinction is purely arbitrary, but so conven- 

 ient that it is practically indispensable ; for it will be seen in a moment, how 

 an otherwise lengthy description can be compressed into, for example, four 

 words : "above, green ; below, yellow :" and these terms are often used 

 because many birds' colors have some such simple general character. 

 The "upper parts" of the body proper (§ 33) have, also, received the gen- 

 eral name of notanim (Gr. notes, back; tig. 4, 12) : the "under parts," simi- 

 larly restricted, that oi gastraium (Gr. gaster, belly; fig. 4, 20). These two 

 are 



§ 37. Never Naked, while both head and neck may be variously bare of 

 feathers. The only exception is the transient condition of certain birds dur- 

 ing incubation : when, either, like the eider duck, they pull feathers ofl- the 

 belly to cover the eggs or even to build the nest, or, like several other birds, 

 the plumage below is worn off in setting. The gastrseum is rarely pecu- 



