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Show 1878.] TRACHEA O F R H Y N C H ^ E A CAPENSIS. 749 the trachea, and the remarkable modification of the intrathoracic rings, to be presently described, had not proceeded so far. 3. Immature females, indistinguishable in point of plumage, though already larger than males. In all of these, without exception, the windpipe was found quite straigbt and simple throughout, though even at this stage females are infallibly to be distinguished from males by their stouter trachea, by the more powerful musculature of this, and by the more inflated condition of the delicate membranes connecting the bronchial half-rings with one another and with the three-way piece. 4. Young, adult, and apparently old males, all agreeing together in plumage and in the straight and simple condition of the trachea. W e shall see that the superficial loop which is invariably to be found in birds belonging to group 1 (old females) is the outward expression, so to speak, of a modification of the intrathoracic tracheal rings that takes place pari passu with those external changes which, when they are completed, mark the adult. But in order to make my description of this curious modification more intelligible, a few words, by way of preface, about the unmodified trachea of the male, or, better, of an immature female. If such a trachea be drawn through the fingers from end to end, a broad and shallow constriction will be felt near its posterior end, twenty rings or so from the compound three-way piece; the rings composing it are cylindrical instead of flattened, more than thrice as numerous as they are in an equal length of any other part of the tube, and so closely packed and firmly bound together as to possess little or none of that power of expansion and contraction which, by reason of their peculiarly bevelled ends, so eminently distinguishes the rest; it occupies a position as much within as without the thorax ; and the great extrinsic muscles which pass between the sternum and the trachea, serving amongst other purposes as "guys" to keep the latter in place, expand and unite sheath-like over it, being inserted into it at numerous points, but especially at its anterior extremity ; it is, in fact, the part of the trachea upon which the sterno-tracheal muscles directly pull when they contract, and thereby approximate the rings of the extensible intrathoracic portion of the windpipe in the adult female, to which we may now return. On more closely examining the extrathoracic portion of the traehea in a bird in which that part is in the condition represented in fig. 1, p. 748, it can be seen that the loop is almost wholly composed of the constricted portion above described, and that the 2 or 3 rings that immediately succeed in order from before backwards (those situated at the point where the tube disappears within the cavity of the chest) suddenly get coarser and more prominent, and at the same time separated from one another by perceptible membranous intervals. On cutting away the sternum so as not to sever the sterno-tracheal muscles from their attachments, and so as to leave the furcula together with the membrane included between its two arms in place, the rest of the tube is displayed in a completely extended condition ; it is then seen that the 12 or 13 rings immediately succeeding the coarser |