548 DR. J. MURIE 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 ventral to the vertebral 
superficies is 2 inches. The elevated smooth ventral aspect is, as noted, moderately deep 
and with biconcave margins. The cesophageal 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 cesophageal 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—0°7 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 synovial 
joint, is a smaller and softer V-shaped cartilaginous body, which, as a whole, includes 
the cartilages of Santorini and Wrisberg. 
ce. Laryngeal Membranes and Ligaments.—The thyro-hyoid membrane, or middle 
thyro-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 hyo-epiglottic 
ligament. 
The lateral thyro-hyoid ligaments are two narrow bands of fibro- 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, divisible by human anatomists into a mesial and two 
lateral crico-thyroid ligaments, is, in Otaria, a well-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, 
