550 DE. J. MUEIE ON THE ANATOMY OF THE SEA-LION. 



membrane. The two cricothyroid muscles converge medianly in front, but leave a 

 triangular interval exposing the crico-thyroid membrane behind. 



Posterior crico-arytenoid. — This is of considerable size and thickness. It covers the 

 posterior surface of the cricoid cartilage, with the exception of the spatular appendix. 

 The fibres expanding outwards and forwards from the above origin are inserted into the 

 outer protuberance of the arytenoid cartilage. As in Man, the outermost fibres are 

 nearly vertical, and the upper or anterior ones nearly transverse to the antero-posterior 

 axis of the larynx. The posterior margin of the thyroid cartilage partially hides the 

 outside curved edge of the posterior crico-arytenoideus. This muscle is a retractor of 

 the arytenoid cartilage and dilater of the glottis. 



Lateral crico-arytenoid. — A short, triangular-shaped muscle lying outside inferiorly, 

 but in close connexion with the last mentioned. It occupies the space anterior to 

 and below the crico-thyroid joint, and is fastened to the prominent protuberant angle 

 of the arytenoid cartilage. The action of this pair of muscles is to drag downward 

 the arytenoid cartilage, and close the posterior lip of the glottis. No ceratocricoid slip 

 of Merkel was observed. 



Thyro-arytenoid. — Divisible in this species of Eared Seal into at least two well- 

 defined bundles: — (a) The larger inferior one is a strong broad plane of muscular fibres 

 which arise from the front and middle of the interior junction of the thyroid alae. 

 Passing towards the arytenoid cartilage the fleshy fibres are inserted in front of (or below) 

 the arytenoid protuberance. A few of the fibres run over the surface of the arytenoid 

 muscle, (b) The superior smaller division in some respects may represent the so-called 

 aryteno-epiglottidean muscle of human anatomy. This portion commences partly by 

 fascia and partly by muscular fibres from the interior of the thyroid cartilage in front 

 of the laryngeal pouch. Splitting so as to lie on either side of the sac and again uni- 

 ting, the muscle is finally inserted into the arytenoid cartilage and cartilage of Santo- 

 rini, anterior, however, to the arytenoid muscle. The superficial division of the thyro- 

 arytenoid in great part covers this second segment. Concerning the function of the fore- 

 going, the large inferior planes (a) of both sides drag forwards the arytenoid cartilages, 

 and therefore approximate the true vocal cords. The superior divisions (b), fixed more 

 behind the arytenoid cartilages, compress the laryngeal sacculus ; but they possibly also 

 drag forwards the Santorine cartilages and close the aperture of the glottis. 



The arytenoidei muscles do not decussate obliquely and pass right across, as they do 

 in Man. In the larynx of Otaria the arytenoid is thick, short, and alone fills the con- 

 cavity of each arytenoid cartilage. 



Appertaining to the hyoid and thyroid region, I may in this place institute record 

 of a thick fleshy muscle, somewhat of a long parallelogram in figure, and situated 

 immediately beneath the posterior end of the hyoglossus and anterior portion of the 

 superior constrictor when the parts are in natural position. The muscle in question 

 has attachments to, and bridges or connects the cerato- and thyrohyal bony segments, 



