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Show 1901.] LARYNX OF CERTAIN WHALES. 297 parallel to the long axis, and, as we have seen, forms the lateral margins of the entrance to the larynx, which, according to Dubois, corresponds to the " glottis"-the rima glottidis of human anatomy. In the case of Cogia this process is less distinctly marked off from the rest. Two further points of interest occur within the Cetacea, viz., the great ventral, sublaryngeal pouch in the Mystacocete, and the peculiar aryteno-epiglottid tube of the Odontocete. I have already referred to the view that the sublaryngeal pouch of the Mystacocete is, in part at least, derived from the tbryo-arytenoid muscle; the great downward " sagging," so to speak, of this muscle, so as to project between thryoid and cricoid cartilage, has led to the oblique and nearly vertical position of the " glottis "-the wide entrance to the laryngeal chamber. This glottis is approached, in these Whales, by a comparatively wide, short canal, owing to the loose connection between the arytenoids aud epiglottis. But in the Odontocete these cartilages are very heavily built, especially at the lower ends ; and that of the epiglottis projects much further into the larynx than in the other group, so that the entrance is reduced to a narrow cleft, and the glottis itself is greatly blocked up by the lower end of the epiglottis. Further, the glottis is not so definitely marked out as in the Mystacocete ; it can be located only by the position of the thryo-arytenoid muscle. One is tempted to see some interrelation between the " pouch " and the "tube"; to think that in some way the junction of the pouch of the Mystacocete is taken on by the glottideal tube and the elaborate " spiracular sacs " of the Odontocete. And this leads us to look for any homologue in tbe Odontocete of the sublaryngeal pouch of the Mystacocete. The latter, as is known, is a median, ventral evagination of the muscular wall of the larynx, between the thryoid and cricoid cartilages ; in position it is post-thryoideal. But in the Odontocete, no outgrowth occurs in the same relative position. It is true that in various genera-e. g. Mesoplodon, Beluga, Grampus-a small median sac has been described by various authors; but this sac has glandular walls (a few muscles are mentioned by Murie), and at any rate occupies a different position, viz., between the base of the epiglottis and the upper (anterior) border of the thyroid cartilage. In fact, it is pre-tlry-roideal in position. Nevertheless, Murie, Watson and Young, and Sir W . Turner, regard this sac as homologous with that of the Mystacocete, and Dubois agrees with them, and, further, includes in the homology small, lateral, glandular outgrowths which occur in some genera (no doubt the conditions represented by Cogia). Now, lateral outgrowths in this position-at the sides of the base of the epiglottis and projecting, more or less, over the upper margin of the thyroid, either actually or morphologically-are known in a great variety of mammals. In some cases the two sacs or "ventricles of Morgagni"are near together and close to |
