REPORT ON THE SPHENISCID.E. 208 



muscle of the upper larynx, while the inner or laryngeal surface is flat, smooth, and 

 covered by the laryngeal mucous membrane. The upper or free border of the cartilage 

 is thin and sharp, and is covered by the dense mucous membrane forming the " laryngeal 

 pads." Connected with the posterior part of this border is a small pointed piece of 

 cartilage, which in some species is quite distinct from, although connected with, the 

 arytenoid cartilage, while in others it is quite continuous with the latter. The lower 

 border of each arytenoid affords attachment to the thyro-arytenoid ligament. The 

 anterior pointed extremity of the arytenoid projects beyond that of the thyroid cartilage, 

 and does not articulate with its fellow, although it is connected with it as well as with 

 the basi-hyal bone, by means of the central thyro-hyoid ligament. The posterior rounded 

 extremity of the arytenoid is provided with a convex articular surface, by means of 

 which it articulates with the upper lateral facet on the cricoid cartilage. 



The Ligaments of the Larynx consist of two thjrro-arytenoid ligaments, by means 

 of which the bases of the arytenoid cartilages are attached to the upper border of the 

 thyroid. The anterior extremities of the arytenoid cartilages are, moreover, connected 

 with one another by means of the central thyro-hyoid ligament, the principal function of 

 which is to attach the anterior pointed extremity of the thyroid cartilage to the basi- 

 hyal bone. The posterior extremities of the arytenoids, as well as the extremities of the 

 thyroid cornua, articulate directly with the cricoid cartilage, the articulation of each being 

 surrounded by a delicate fibrous capsule. 



The Intrinsic Muscles of the upper larynx are two in number, a sphincter and 

 apertor. 



Tlie Si^hincter Laryngis (PL XVIII. fig. 4) is symmetrically disposed on either side of 

 the laryngeal aperture, and is situated immediately beneath the laryngeal pads. The 

 muscular fibres arise on either side of the middle line, from the posterior extremity and 

 posterior half of the outer surface of each thyroid cornu, the origin of the muscle 

 corresponding closely to the insertion of the claviculo-thyroid muscle. The fibres pass 

 obliquely forwards and inwards toward the middle line, and are inserted into the anterior 

 half of the outer surface of each arytenoid cartilage. The external fibres of opposite 

 muscles become continuous with one another in front of the arytenoid cartilages, and 

 thus complete the sphincter arrangement. The sphincter laryngis apparently closes the 

 aperture of the larynx by approximating the arytenoid cartilages. 



The Apertor Laryngis (PL XVIII. figs. 4, 5) consists of two lateral halves, which 

 come into contact posteriorly, and thus form a single muscular mass which separates the 

 origins of the two halves of the sphincter laryngis. The muscle of each side arises in 

 front from the anterior three-fourths of the upper margin of the thyroid cartilage. It 

 passes obliquely backwards and inwards, and is inserted into the posterior half of the 

 outer surface of the arytenoid cartilage, as also into the posterior hoUowed surface of the 

 cricoid cartilage, where the fibres of opposite muscles become almost continuous with one 



