OCR Text |
Show 1881.] TRACHEA IN THE " RATITE " BIRDS. •81 Bifurcating trachea of Apteryx mantelli, from before. Fig. 4. The same, from behind. About twice the natural size. plete in the middle line behind; it is slightly wider and stronger than the preceding rings. The first two bronchial semirings on each side closely resemble it in form ; the first semirings of opposite sides are almost in contact at both extremities, the next pair being more widely separated at those joints. There is only a narrow space between the last tracheal and the first bronchial ring. The succeeding bronchial semirings are perfectly simple, rather deep and stout pieces of cartilage, separated by narrow interannular spaces, and completed internally by a broad memBrana tympanifornis; nowhere do they become complete circles. As in Struthio, there is no pessulus, and no intrinsic muscle. There is a slight antero-posteriorly directed vertical fold of mucous membrane between the two bronchial apertures internally, and also a feebly developed vocal cord on the external wall of the bronchi, where they diverge from the trachea. The lateral muscles stop some way before the end of the trachea, at the place where the stemo-tracheales are inserted. Apteryx australis, A. haasti, and A. oweni have all been |