OCR Text |
Show 1886.] GEOCOCCYX CALIFORNIANUS. 487 The interval thus formed, which is not very great, is occupied by a thin membrane which is continuous with the internal tympaniform membrane of the lower larynx. As to shape, the trachea diminishes in calibre gradually from above downwards, and nowhere in its continuity does it present any enlargements or dilatations. This does not apply exactly to the bronchial bifurcations, for each one of them shows a disposition to swell just before arriving at the contracted parts of these tubes, where they impinge upon the lung-tissue. W e may reckon either of these bifurcations as being partially surrounded by 13 semirings. Of course in this bird, as I say, the entire trachea may be regarded as having only semirings, but had the usual number of these united behind, there would still have remained the 13 semirings to each bronchial tube. An osseous pessulus is not present in Geococcyx, and the internal tympaniform membrane is quite extensive. There does not even seem to be any thickening of this membrane in our subject where this bony little bridge is located in those birds where it exists. As to its myology, the lower larynx is exceedingly simple in arrangement and meagrely supplied. Viewing the inferior part of the trachea and the bronchial tubes from in front, we can see but one pair of muscles, and these are the delicate sterno-tracheales. They are attached on either side to the last five tracheal rings (fig. 3, Plate XLIII.) ; the insertion seemingly consisting of two slips, the inferior one being attached to the lowermost of the five rings. These muscular slips soon merge with each other; and the muscle itself stretches across in the usual manner, for attachment to the inner surface of the costal process of the sternum. From a near view we discover another pair of muscles ; these are the tracheo-laterales (fig. 4, Plate XLIII.). They here extend the whole length of the tracheal tube, on its postero-lateral aspect, rather than fairly on its sides, as in the majority of birds. O n either side they are carried down clear to the last bronchial semiring for attachment, i. e. not reckoning the aforesaid few semideveloped rings which we find at the terminal extremities of these bronchial bifurcations. This position of the tracheo-lateralis muscle is just the reverse of what Garrod found in such a bird as Opisthocomus (Scientif. Mem., p. 466, fig. 1) ; for, according to this authority, these muscles m a y be seen in the Hoatzin on an anterior view, and, moreover, in it they pass down in front of the sterno-trachealis. Garrod made many excellent examinations of the thoracic extremity of the trachea in the Gallinae, and among the representatives of this group an extraordinary variety of forms of this part of the bird's economy was discovered (P. Z. S. 1879, p. 354). As the paper I refer to is profusely illustrated by drawings of the gallinaceous trachea, I have been enabled to compare them with the corresponding parts as I found them to exist in Geococcyx. But of all the types given, I fail to find a single one that in any way resembles the subject before us. This is the less to be looked for, however, when we come to |