| OCR Text |
Show 282 PROP. W. B. BENHAM ON THE [Apr. 2, omitted to notice a fold-sufficiently large, according to these authors, to be drawn over the aditus laryngis-if it had existed. The drawings given by these authors are small and indistinct, and from an inspection of them I was inclined to regard this " fold " as the epiglottis itself; but their account in the text is quite precise, and from the size of the " fold" in the adult it is remarkable that it does not exist in the young. The general form of the larynx is shown in figs. 1, 2, 3, as seen in various aspects. It is of greater diameter from side to side than in the dorso-ventral direction, and the aryteno-epiglottid apparatus is relatively short, as compared with the long tube in the Odontocete. The base of the larynx passes gradually into the trachea, the rings of which are incomplete on the ventral surface. The windpipe is, of course, very short, aud there is no " third bronchus " (nor is there in Balcena), such as will be seen in Cogia. It will be convenient to describe the cartilages first, and then refer to the muscles connected with them. The Cartilages. In dealing with the topographical relations, the larynx is supposed to be still within the body of the animal, which is in its natural position, back upwards. The thyroid cartilage consists of a distinct body and paired posterior cornua. The body is a transverse, narrow7 band, i. e., it has a very short antero-posterior diameter ; its anterior margin is concave, its posterior convex, but with a median V-shaped notch. At the extreme right and left extremities, where the body becomes continuous with the cornua, the anterior margin is thicker and more prominent than elsewhere ; the ridge-like tubercle so formed probably represents an anterior cornu; just below it is inserted the sterno-thyroid muscle. Opposite this ridge-like tubercle, the body of the thyroid curves abruptly backwards, and forms the conspicuous long posterior cornu on each side. This is a stout rod, curved as it passes backwards (i. e. posteriorly) with a rather strong convexity towards the dorsal surface; it is, of course, articulated at its hinder end with the cricoid cartilage. Whereas the body of the thyroid is flat and band-like, the cornu, though of the same character at its origin, soon becomes a thick subcylindrical rod. It is 4 inches long, measured from the anterior margin of the body to the posterior end of the cornu. The body of the thyroid measures 5 inches from side to side; measured from the outer extremities its antero-posterior width (i. e. length) is about one inch, though this becomes greater towards the middle; the depth of the notch is \ inch; a line from the bottom of the notch to the anterior margin, on the median line, measures g inch. |
