532 



RESPJBATOBY APPARATUS IN MAMMALIA. 



by proper muscles, which either produce its total displacement, or cause the 

 several cartilages to play upon each other. Among these muscles there are three 

 extrinsic — the sterno-thijroideus, hyo-thyroideus, and the hyo-epiglottideiis. The 

 others are intrinsic, or attached in their origin and termination to the different 

 pieces of the larynx ; they are — the crico-thyroid, iMsterior crico-aryUmoid, lateral 

 crico-aryictnoid, thyro-arytoenoid, and the arytmioideus muscles. All are pail's, 

 except the last and the hyo-epiglottideus. 

 Sterno-thyroideus. — (See p. 255.) 



Hyo-thyroideus (Fig. 314, 3). — This is a wide, triangular muscle, formed 

 entirely of muscular fasciculi, which arise from the whole extent of the hyoid 

 cornu, and terminate on the external face of the thyroid ala ; the most inferior 



are longest. This muscle covers the 

 Fig. 314. thyroid cartilage and the thyro- 



hyoid membrane. It is covered by 

 the maxillary gland.^ 



In contracting, this muscle 

 brings the thyroid cartilage within 

 the branches of the hyoid bone, and 

 in this way carries the larynx for- 

 ward and upward. 



Hyo-epiglottideus. — This is 

 a small cylindrical fasciculus, the 

 fibres of which are buried in the 

 middle of a mass of adipose tissue, 

 and extend from the superior sur- 

 face of the body of the hyoid bone 

 to the antero-inferior face of the 

 epiglottis. Partly covered by the 

 mucous membrane of the pharynx, 

 this muscle concurs in restoring the 

 epiglottis to its normal position 

 after the passage of food or water 

 over it. But it is also necessary 

 to state that the epiglottis is 

 caiTied forward more particularly by its o\vn proper elasticity, as well as that of 

 the ligamentous bands that attach it to the thyroid cartilage. 



Crico-thyroideus (Figs. 314, 11 ; 315, 8). — This small muscle, applied to 

 the external side of the cricoid cartilage, is elongated from above to below, and 

 composed of somewhat tendinous fibres which cross, more or less, the general 

 direction of the muscle. They arise from the above-named cartilage, and pass 

 to the posterior border of the thyroid plate. 



The crico-thyroideus shortens the larynx, in bringing together the two 

 cartilages into whicli it is inserted. 



Posterior Crico-arytenoideus (Figs. 314, 315, 5). — This is the most 

 powerful muscle in this region. Its fibres are directed forwards and outwards, 

 ' and arise from the bezel of the cricoid, Avhich they cover, and from the median 

 crest of that part. They all converge, in becoming more or less tendinous, 

 towards the posterior tubercle of the aryt^enoid cartilage, on which they termi- 

 Bate. Covered by the oesophagus and the crico-pharyngeal muscular band, this 

 (' This and the precediag muscle are usually described as one — the sterno-thyro-kyoideus.) 



MUSCLES OF THE HORSE S LARYNX. 



1, Hyoideus transversus; 2, kerato-hyoideus ; 3, hyo- 

 thyi'oideus ; 4, sterno-thyroideus ; 5, crico-arytse- 

 noideus posticus ; 6, crico-arytsenoideus lateralis ; 

 7, arytaenoideus ; 8, posteiior fasciculus of the 

 thyro-arytanoideus ; 9, anterior fasciculus of ditto; 



10, lateral ventricle of the larynx artlKcialiy dis- 

 tended and projecting between the two fasciculi ; 



11, crico-thyroideus 



