37 



membrane ; exterior to this fold the pharyngeal membrane is puck- 

 ered up into numerous minute irregular plications, in the intervals 

 of which are the orifices of numerous mucous follicles, which are also 

 scattered about the immediate neighbourhood of the glottis. 



" In the largest Dugong dissected (No. 2.), the thyroid, cncoid, and 

 arytenoid cartilages presented several bony granulations, scattered 

 irregularly through their substance : in older animals their ossification 

 may become more complete. 



" The mesial fissure, which is commonly pi'esent in other Mammalia 

 at the inferior margin of the thyroid, is here continued through the 

 whole of that cartilage, dividing it into two distinct lateral moieties, 

 connected above by dense fibrous texture, and below by membrane 

 merely and cellular and adipose tissue. Each portion presents an 

 irregular elongated rhomboidal figure, of which one extremity forms 

 the point of junction with its fellow above-mentioned, while the oppo- 

 site angle is prolonged into the inferior cornu, and is similarly 

 and closely connected by a strong ligament to a prominence on the 

 side of the cricoid cartilage ; the intermediate angle on the posterior 

 margin of the thyroid feebly represents the superior cornu. Length 

 of the thyroid cartilage, 2 inches 9 lines ; breadth of each lobe, 1 inch 

 3 lines. The cricoid cartilage is the lai^gest ; it forms a complete 

 ring. The broad posterior surface is not rounded, but bent so as to 

 offer three facets, one narrow in the middle, which expands above 

 and below, and two broad lateral ones ; and the inferior margin de- 

 scribes three straight lines. The superior margin is very thick, and 

 presents on each side an elliptical, convex, articular surface for the 

 arytenoid cartilage. The anterior margin of the cricoid is rounded 

 and convex, and slightly notched above. Longitudinal diameter of 

 the cricoid posteriorly, 1 inch 9 lines ; ditto anteriorly, 8 lines : cir- 

 cumference of cricoid, 6 inches. Each arytenoid cartilage is in form 

 of a short irregular three-sided pyramid ; the inner surface flat, the 

 anterior and outer surface convex ; the posterior and outer surface 

 concave ; the base is excavated, to fit the articular convexity of the 

 cricoid, with which it is connected by a synovial and fibrous capsule ; 

 the apex is compressed and extended in the antero-posterior direc- 

 tion ; it forms the convex lateral margin of the glottis above de- 

 scribed. A short space, however, intervenes between the anterior 

 part of the arytenoid, and the thyroid cartilages, which is occupied 

 as usual by an elastic, dense, and pretty thick chorda vocalis, and 

 the investing laryngeal membrane. There is a small pit between 

 the anterior attachments of the chorda, but no sacculus is developed 

 from this or any other part of the larynx. The mucous membrane 

 of the larynx is smooth for the extent of five lines after it is re- 

 flected over the apical margins of the arytenoid cartilages, and then 

 begins suddenly to be disposed in numerous narrow pZ/cfi", which in- 

 crease in breadth as they descend into the trachea, and are arranged 

 somewhat obliquely, diverging in a penniform manner from the mid- 

 dle line of the anterior surface of the tube. At the back part of the 

 larynx and trachea these ruga are longitudinal. 



"The epiglottis cannot be said to exist as a distinct cartilage in the 



