444 RESPIRATORY SYSTEM OF THE HORSE 



of elastic cartilage; they show no tendency toward ossification at any age. The 

 thyroid and cricoid cartilages regularly undergo considerable ossification; the 

 process begins in the body of the thyroid, and often involves the greater part of 

 the cartilage. 



Joints, Ligaments, and Membranes of the Larnyx 



The crico-thyroid joints (Articulationes crico-thyreoidese) are diarthroses 

 formed by the apposition of the convex facets on the ends of the posterior cornua 

 of the thyroid cartilage with corresponding facets on the sides of the cricoid car- 

 tilage. The capsule is thin, but is strengthened by accessory bands dorsally, 

 externally, and internally. The movements are chiefly rotation around a trans- 

 verse axis passing through the centers of the two joints. 



The crico-arytenoid joints (Articulationes crico-arytsenoidea) are also diar- 

 throdial. They are formed by the apposition of the convex facets on the anterior 

 border of the cricoid cartilages with the concave facets on the bases of the arytenoid 

 cartilages. Each has a very thin, loose capsule, strengthened by accessory bundles 

 dorsally and internally. The movements are gliding and rotation. In the former 

 the arytenoid cartilage glides inward or outward; in the latter it rotates around a 

 longitudinal axis, so that the vocal process swings outw^ard or inward. 



The thyro-hyoid joints (Articulationes hyo-thyreoidese) are formed by the 

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

 of the hyoid bone. They permit rotation around a transverse axis passing through 

 the two joints. 



The crico-thyroid membrane (Ligamentum crico-thyreoideum) occupies the 

 thyroid notch and extends backward to the arch of the cricoid cartilage. It is 

 triangular 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 thyroid notch. 



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

 terior border of the thyroid cartilage with the l)ody and thyroitl cornua of the hyoid 

 bone. 



The hyo-epiglottic ligament (Ligamentum 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 (Ligamentum 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 inner surface of the laminae of the thyroid 

 cartilage. Other fibers attach the cuneiform processes somewhat loosely to the 

 thyroid laminae. 



The transverse arytenoid ligament (Ligamentum arytaenoideum transversum) 

 is a slender band which connects the inner angles of the bases of the arytenoid 

 cartilages. 



The vocal (or inferior thyro-arytenoid) ligament (Ligamentum vocale) forms the 

 basis of the true vocal cord (Fig. 254), It is 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 superior thyro-arytenoid) ligament (Ligamentum ventri- 

 culare) is included in the false vocal cord. It consists of loosely arranged bundles 

 which arise chiefly from the cuneiform process and end on the outer surface of the 

 processus vocalis and adjacent part of the arytenoid cartilage. 



