OCR Text |
Show 284 PROF. W. B. BENHAM ON THE [Apr. 2, " process," and of a thin lamelliform, antero-ventrally placed " wing." (PI. X X V I I . fig. 15.) Of these, the body and the " wing" are visible from without, after removal of the muscles, while the posterior " process " can only be seen by removal of the wall of the larynx. The " body," or processus muscularis, of the arytenoid is somewhat conical, with an obtusely rounded apex directed forwards and outwards (PI. X X V . fig. 2) ; the base-measuring 1 £ inches-is narrow and elongated transversely ; it articulates with the cricoid in a typical fashiou at the antero-lateral dorsal margin of the latter; its apex serves for the insertion of the crico-arytenoid muscles. The anterior " wing-like " process (= supra-arytenoid of Thompson) rises from the body by a comparatively thick basal region, but this soon becomes a thin plate, which is somewhat crescentic in form-the form is, after all, best appreciated by a study of the figures. One horn of the crescent is directed forwards and dorsally, and the right and left" wings " approach one another at their extremities, supporting the " arytenoid bodies." The posterior half of the crescent is continuous with the posterior process of the arytenoid: the convex margin of the " wing " is directed inwards, towards the cavity of the larynx ; its extreme edge is reflected outwards, and the whole of the lower half of the wing is set at an angle with the plane of the posterior process, so that a " fossa " is enclosed by them. In this fossa, to the external concave face of the arytenoid wing, are inserted the upper portions of the aryteno-epiglottidean muscles. The third part of the arytenoid, the posterior " processus vocalis," arises from the body by a broad stout base; its long axis is directed backwards, parallel to its fellow, close to the dorsal wall of the larynx. In addition to serving for the insertion of the lower aryteno-epiglottidean muscles and the thyro-arytenoids, these two processes form the margins of the true entrance into the laryngeal sac. The total length of the arytenoid is 4 inches, measured in a straight line from the anterior end of the " wing " to the posterior tip of the " process." In the Greenland Bight Whale the two processus vocales of the arytenoid cartilages are continuous at their distal ends, forming a posterior support for the laryngeal opening; this is not the case iu the young Borqual, though the ends were connected by dense connective tissue, and very probably this became replaced by cartilage in older animals. The epiglotiid cartilage is embedded in the aryteno-epiglottid and other muscles, so that only a small piece of it comes to the surface. On dissection, however, the cartilage is found to have the usual form (PI. XXArI. figs. 11, 12), resembling a shoe-horn ; it consists of an upper thin plate (a) with a wide shallow- groove, and a lower thicker moiety (b) which is connected by fibrous tissue |