. A history of British birds . ube, it passesout under the arch of the merrythought; where, turningupwards, and afterwards backwards, it enters the body ofthe bird to be attached to the lungs in the usual is the state of development in the oldest bird theAuthor met with. The degree next in order, or younger,differs in having the horizontal loop of the trachea confinedto one side only of the cavity in the sternum, both sides of BEWICKS SWAN. 321 the cavity being at this time formed, although the loop ofthe tube is not yet sufficiently elongated to occupy the wholespace. The third an
. A history of British birds . ube, it passesout under the arch of the merrythought; where, turningupwards, and afterwards backwards, it enters the body ofthe bird to be attached to the lungs in the usual is the state of development in the oldest bird theAuthor met with. The degree next in order, or younger,differs in having the horizontal loop of the trachea confinedto one side only of the cavity in the sternum, both sides of BEWICKS SWAN. 321 the cavity being at this time formed, although the loop ofthe tube is not yet sufficiently elongated to occupy the wholespace. The third and right-hand one of the three represen-tations below, from a still younger bird, possesses only thevertical insertion of the fold of the trachea; yet in thisspecimen the cavity in the posterior portion of the sternumalready exists to a considerable extent. The above are the peculiarities of structure belonging tothe tube and the sternum. The bronchige are very short;but the flexible part intervening between the bone of divari-. cation and the bronchial rings is considerable, producing aneffect to be hereafter noticed ; this elongated, flexible, anddelicate portion being defended on each outer side by a dis-tinct membrane, attached to the whole edge of the bone ofdivarication, and to a slender semicircular bone on each side,by which it is supported. The muscles of voice with which this bird is providedpass down—as usual—one on each side of the trachea, tillthe tube is about to enter the cavity in the keel; they thenqait that part of the tube to be attached to the ascending VOL. IV. T T 322 ANATIDiE. portion of the curve, which they follow, ultimately dividinginto two slips, one of which—inserted upon the surface of thebone of divarication—governs the length of the precedingflexible portion of the tube ; the other slip passes off down-wards to be attached to the inner surface of the breast-bone,anterior to the first rib. The course of the muscle on oneside may be traced i
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Keywords: ., bookauthorsaun, bookcentury1800, bookdecade1870, booksubjectbirds
