OCR Text |
Show 1899.] INTERNAL ANATOMY OF NOTORNIS. 93 as does the ovary, the immaturity of the bird. The so-called " thyroid" (which, according to Gadow, is the " cricoid " of recent authorities) is a nearly flat, somewhat spoon-shaped, plate (a), slightly convex ventraily, especially posteriorly ; it is feebly pointed in front and truncated behind. The posterior half of its lateral margin is slightly upcurved and forms a cartilaginous ridge, with which is articulated a second bony plate (b), which is separated from (a) by a narrow cartilaginous area. The posterior piece (b) belongs apparently to the "thyroid," with which it becomes continuous, according to Tiedemann and Dumeril, in very old birds. The piece b curves sharply iiiAvards dorsally, and articulates with the side of a small median bone (d), the " cricoid " (or " pro-cricoid " of Fiirbringer) ; it is hexagonal in shape, with the anterior side largest and a groove along the middle ; its lateral edge articulates with the incurved margin of the plate b, Avhile its anterolateral angle of each side supports the hinder end of the " arytenoid " (c). The arytenoid is again imperfectly ossified, as is indicated in the figure; it is a Y-shaped bone, with the middle limb directed forwards, and it appears to be here connected Avith the epiglottis, but of this I am uncertain. I only cleaned the left side of the larynx, as of the syrinx', as I did not Avish to do more injury than was necessary. The main part, and stronger half, of the bone articulates with the " cricoid," while the feebler, and at present cartilaginous, limb (c) of the Y supports the margin of the glottis and ends freely behind. As to the musculature of the larynx, I am unable to say anything, as I did not think any important point would be presented by its arrangement. The rings of the trachea are only partially ossified ; they overlap one another alternately right and left (fig. 4), and are, of course, narroAver in the middle line dorsally and ventraily. Overlying this region, on the dorsal line, is a small nodule of cartilage (x). (d) The Syrinx (figs. 4-6, pp. 94, 95, 96) consists of seven closely-apposed rings (a-g), of Avhich the fourth (d) carries the pessulus, so that I presume, from Gadow's account of the structure in general, this ring should be regarded as the last tracheal. If this be the case, then four of the syringeal rings are tracheal and three are bronchial. The " membrana tympaniformis externa " is supported by the last syringeal ring (g) and by the three folloAving bronchial rings (I, II, III). The rings of the syrinx (a-g) are in the present specimen separate, OAving no doubt to the growth of the bird. As the arrangement of these rings is unlike anything figured by Gadow in " Bronn," I will describe the syrinx in some detail. The ring a differs little from the preceding normal tracheal ring (1), which, indeed, overlaps it on the right side. The next rino- (b) is, hoAvever, incomplete dorsally, where its end is enlarged and abuts upon a cartilaginous plate, in the centre of Avhich is a small nodule of bone (y). |