518 RESPIRATORY SYSTEM OF THE HORSE 



dorsally and medially. The most important movement is rotation of the arytenoid 

 cartilage about a longitudinal axis so that the vocal process swings outward (ab- 

 duction) or inward (adduction), carrying the vocal cord with it. Another move- 

 ment here is rotation about a transverse axis, in which the apical part of the carti- 

 lage is raised or lowered. The arytenoid is also capable of slight inward or outward 

 gliding movement. 



The thyxo-hyoid joints (Articulationes hyo-thyreoideae) are formed by the 

 anterior cornua of the thyroid cartilage and the cartilaginous extremities of the 

 thyroid cornua of the hyoid bone. They are diarthroses and the joint capsule is 

 reinforced by a relatively strong thyro-hyoid ligament. The thyroid cornu has 

 here a cartilaginous prolongation about a quarter of an inch (ca. 6 mm.) in length. 

 The chief movement is rotation around a transverse axis passing through the two 

 joints. 



The crico-thyroid membrane (Membrana crico-thyreoidea) occupies the thy- 

 roid notch and extends backward to the arch of the cricoid cartilage. It is tri- 

 angular in form, and is attached by its base to the anterior border of the arch of 

 the cricoid cartilage, while its borders are attached to the margins of the thyroid 

 notch. It-is strong, tightly stretched, and composed largely of elastic tissue. It 

 is reinforced ventrally by longitudinal fibers, dorsally by fibers which stretch across 

 the thjToid notch. 



The thyro-hyoid membrane (Membrana hyo-thyreoidea) connects the body 

 and anterior borders of the thjrroid cartilage with the body and thyroid cornua of 

 the hyoid bone. 



The hyo-epiglottic ligament (Lig. hyo-epiglotticum) attaches the lower part 

 of the oral surface of the epiglottis to the body of the hyoid bone. It forms an 

 elastic sheath for the hyo-epiglottic muscle. Ventrally it blends with the thyro- 

 hyoid membrane, and dorsally it is not well defined. 



The thyro-epiglottic ligament (Lig. thyreo-epiglotticum) is strong and thick; 

 it is composed chiefly of elastic tissue. It connects the base of the epiglottis with 

 the body and the adjacent medial surfaces of the laminte of the thyroid cartilage. 

 Other fibers attach the cuneiform processes somewhat loosely to the thyroid laminaj. 



The transverse arytenoid ligament (Lig. arytsenoideum transversum) is a 

 slender band which connects the medial angles of the bases of the arytenoid carti- 

 lages. 



The vocal (or posterior thyro-arytenoid) ligament (Lig. vocale) underlies and 

 is intimatety adherent to the mucous membrane of the true vocal cord. It is thin 

 and elastic and is attached ventrally to the body of the thyroid cartilage and the 

 crico-thyroid membrane close to its fellow of the opposite side, and ends dorsally 

 on the processus vocalis of the arytenoid cartilage. 



The ventricular (or anterior thyro-arytenoid) ligament (Lig. ventriculare) is 

 included in the false vocal cord. It consists of loosely arranged bundles which 

 arise chiefly from the cuneiform process and end on the lateral surface of the pro- 

 cessus vocalis and adjacent part of the arytenoid cartilage. 



The crico-tracheal membrane (Membrana crico-trachealis) connects the cri- 

 coid cartilage with the first ring of the trachea. 



Muscles of the Larynx 

 A. Extrinsic Muscles 

 The stemo-thyro-hyoideus is described on p. 268. 



The thyro-hyoideus (M. hyo-thyreoideus) is a flat, quadrilateral muscle, which 

 lies on the lateral surface of the thyroid lamina and the lateral part of the thyro- 

 hyoid membrane. It arises from the body and thyroid cornu of the hyoid bone 

 (almost meeting the opposite muscle), and ends on the oblique line on the lamina 



