OCR Text |
Show 356 PROF. A. H. GARROD ON THE [Apr. 1, ring of the trachea. The last tracheal ring, it must not be forgotten, is incomplete behind. The first bronchial semiring-for in no Gallinaceous birds are any of the bronchial rings complete-articulates at both its extremities with the last tracheal, anteriorly along the side of the oblique median process, posteriorly with the lower angle of its square-cut termination. Both ends are slightly expanded and obliquely truncated, their acute upper angles being their articulating spots. The lower margin of the last tracheal ring being concave downwards and slightly uptipped laterally, whilst the first bronchial semiring descends slightly from its attachments outwards, a considerable membranous interannular interval is left. The second bronchial semiring is simple, free, and slightly expanded posteriorly. In front the third was bifurcated in both bronchi, on one side each branch being further subdivided. The depth of the bronchial interannular membranes is about the same as that of the semirings themselves. Between the membranous inner wall of one bronchial tube and the same part of the other there is a dense fibrous band of union, a short distance below the bifurcation of the windpipe, and generally on the level of the two or three semirings below tbe second. This band is, 1 believe, always to be found in birds (it will be termed the bronehidesmus in this communication) developed to a greater or less extent. Being of fibrous tissue and connected with the membranes of the neighbourhood, anatomists have removed it whilst dissecting the organ for examination. Its importance, however, is more considerable than might be at first imagined ; and I only regret that in many of the subjoined descriptions I took no note of it. In birds like the Tetraonidae the bronehidesmus is so strong that it cannot escape special observation. The adult female presents no modifications' of importance. The penultimate and last tracheal rings are relatively a little smaller and have blended in front in tbe middle line, whilst all trace is lost of the shape of the posterior termination of the pessulus. The articulating surfaces of the first bronchial semiring have become slightly more considerable. The adult (male) P. nigripennis differs in that the antepenultimate tracheal ring blends anteriorly with the penultimate, at the same time that there is a greater fusion between the penultimate and last rings, all three apparently blending behind as well. The interannular interval between the last tracheal ring and the first bronchial semiring is reduced to little more than a line, and the bronchial interannular intervals are very small. It is to be specially noted that in the genus Pavo the second bronchial semiring, by not articulating with the one above it at either end, does not participate in the formation of the specialized lower larynx. This is a feature indicating non-elaboration of the organ. No other Gallinaceous bird with which I am acquainted resembles Pavo in this respect. In Caccabis rufa the thoracic extremity of the trachea is perfectly |