OCR Text |
Show 288 PROP. W. B. BENHAM ON THE [Apr. 2, II. T H E LARYNX OF COGIA. From the few references to this small Cachalot that I able to discover, I gather that very little is known of its viscera. The larynx agrees on the whole with that of other Odontocetes hitherto described in detail, but in certain points-as, for instance, and in particular, iu the duplicity of the thyroid cartilage- it appears to be unique amongst the Cetaceans, at least so far as is indicated in the small amount of literature available and references therein. The specimen to which this larynx belonged had, as I have stated above, been cut open and injured in various ways before I was able to obtain possession of the carcase, and the larynx itself had been cut through and severed from the pharynx and from the hyoid bone, hence I a m unable to give an account of the relations of the organ to the neighbouring parts ; but, as these are well known for several other genera, this deficiency is of little importance. The general form of the larynx is seen in the accompanying drawings (PI. X X V . figs. 4, 5, PI. X X V I . fig. 6). It has a greater diameter dorso-ventrally than laterally, which is the reverse of the condition in Balcenoptera and in Globiocephalus melas, according to Murie (1867). Its dorso-ventral diameter (3 inches) is much greater than that of the trachea (1| inches), so that the postero-ventral margin projects considerably and forms a veritable "pomum adami." From the upper and anterior end of the larynx the conjoined arytenoids and epiglottid cartilages project as a distinct tube, and this characteristic Odontocete tube is directed upwards and forwards towards the dorsal surface; this makes a very distiuct angle with the longitudinal axis of the laryngeal cavity, whereas in the Borqual the arytenoids and the epiglottis diverge from one another, each forming an angle with the axis of the larynx, but in opposite directions. The "aryteno-epiglottidean tube" projects upwards from the floor of the pharynx for about \\ inches. The upper end is thickened so as to be firmly clasped by the velum palati and retained within the narial canal; it had been cut away from its natural position, so that the relation of the end of the tube to the nares could not be ascertained, though there is no reason to believe it to be different from what has been described for other Odontocetes. The aditus laryngis (PI. XXArlI. lig. 20), when stretched to its fullest extent, is somewhat rectangular, with thickened, rounded margins ; the lateral margin on each side is formed by the thick and fleshy " aryteno-epigiottid " fold, which reaches upwards to the apex of each of the cartilages concerned ; the dorsal margin by the rounded edges of the two arytenoid bodies, which are continuous along their dorsal surfaces right to their tips, and are in strong contrast with those of Balcenoptera, for in place of their lamelliform separable plates, we have in tbe Odontocete a thick, rounded or continuous fold. The ventral margin of the aperture |