548 DE. J. MmiE ON THE ANATOMY OF THE SEA-LION. 



Behind it is 2 inches in extreme (antero-posterior) depth; in front, or superficially, 

 which is the narrowest part, it is 0'9 inch ; the diameter from the A'entral to the vertebral 

 superficies is 2 inches. The elevated smooth ventral aspect is, as noted, moderately deep 

 and Avith biconcave margins. The oesophageal surface has a raised mesial line, with 

 lateral, wide, shallow excavations between it and the thyroid cartilages, the posterior 

 crico-arytenoid muscles completely filling these depressions. Where the arytenoid 

 cartilages are attached the cricoid on each side is very much thickened and projects in 

 a rounded manner, leaving a median deep cleft or notch, which is filled with fibro-fatty 

 tissue. The tracheal end of this same oesophageal surface has a thin spatulate cartila- 

 ginous plate 0-3 inch long, and fully as much broad at its widest part. On each side of 

 this the borders are incised semilunarly, and form a slight angle posterior to (or beneath) 

 the thyro-cricoid articulation. 



Each pyramidal or trihedral, but round-margined arytenoid cartilage is of the fol- 

 lowing dimensions — 07 inch in extreme height, an inch in basal width, and 0'6 inch 

 in thickness, or from the internal to the external surface. Its crico-articulating facet 

 is large, shallow, and with a synovial membrane. The inner mesially connecting spur 

 is the thinnest and most elastic portion, and possesses a rounded recurved point to which 

 the interarytenoid ligament is fixed. The true and false vocal cords have a firm and 

 strong bond of union. The posterior crico-arytenoid ligament loosely but powerfully 

 connects the cartilages in the interval. 



Fixed to the summit of the arytenoid cartilage by a close, movable, but not syno^dal 

 joint, is a smaller and softer V-shaped cartilaginous body, which, as a whole, includes 

 the cartilages of Santorini and Wrisberg. 



c. Laryngeal Membranes and Ligaments. — The thyro-hyoid membrane, or middle 

 tliyro-hyoid ligament, forms a strong, wide, and very elastic connecting bridge between 

 the basihyal, thyrohyals, and thyroid cartilage. It contains in its centre, or midway 

 between the basihyal and the fore part of the thyroid shield, a firm, well-developed, 

 cartilaginous nodule. This nodule of cartilage has a short figure-of-8 shape, smooth 

 on the ventral surface, and rougher or somewhat carinate anteriorly on its deep aspect. 

 It is 0-8 inch long, and 0-5 broad at its anterior segment. It is deeply imbedded in the 

 fat and fibrous tissue at the root of the epiglottis ; and between the latter and its internal 

 projecting anterior point there passes a strong fibro-elastic band — the kyo-ejii glottic 

 ligament. 



The lateral thyro-hyoid ligaments are two narrow bands of fibre- and yellow elastic 

 tissue, which pass between the tip of the thyrohyals and each cartilago triticea to the 

 short anterior cornua of the thyroid cartilage. 



The crico-thyroid membrane, di\'isible by human anatomists into a mesial and two 

 lateral crico-thyroid ligaments, is, in Otaria, a weU-developed strong fibro-elastic struc- 

 ture, the median portion containing abundance of yellow elastic tissue, which is thick- 

 ened and forms a projecting ridge. The lateral portions of the crico-thyroid membrane. 



