RESPIRATORY SYSTEM 



763 



In the mammals one or more thyroid cartilages are added on the 

 dorsal side to those already described. In the monotremes the hyoid 

 apparatus and the larynx are most intimately connected, but in the 

 higher forms of mammals such an association is not so intimate even in 

 the embryo. 



The thyroid cartilage forms a half ring on the ventral side of the 

 anterior end of the larynx in the higher mammals. The anterior dorsal 

 angles form cornua which connect with the hyoid by a ligament. Dorsal 



A. 



Fig. 442. 



A, Muscles of larynx (voice box) of Rana esculenta. Dorsal view, aryt., 

 arytenoid cartilage ; dtt.lar., dilator muscle ; hy.lar., hyo-laryngeus muscle ; 

 lig.i.crie., intercricoideum ligament ; s., tendon of posterior sphincter muscle ; 

 sph.ant., anterior sphincter muscle ; sph.post., posterior sphincter muscle. 



(After Gaupp.) 



B, Laryngeal apparatus of a Turtle, ar, arytenoid ; 6 1 - 2 , first and second 

 branchial arches ; cr, cricoid ; d, dilator laryngis muscle ; g, glottis ; h, hyoid ; 

 he, hyoid cornua ; sph, sphincter laryngis ; tr, trachea. Cartilage is dotted, 

 bone is black. (From Kingsley, after Gb'ppert.) 



to the thyroid is the glottis with the arytenoids in its walls. Posterior 

 to the glottis is the ring-shaped cricoid, which is followed by the trachea. 

 Anterior to the glottis lies the epiglottis, which is a fold of mucous mem- 

 brane supported by an internal cartilage which articulates with the an- 

 terior margin of the thyroid. Trie epiglottis usually stands erect, thus 

 leaving the glottis open during respiration, while during deglutition it is 

 pulled back into the glottis, supposedly preventing the entrance of food 

 into the trachea, but there are numerous cases on record where the epi- 

 glottis has been removed and such individuals seem to have no difficulty 

 with their food getting into the "wrong throat." 



The cavity of the larynx bears a vocal cord on either side internally. 

 These are folds of the mucous membrane which extend from the thyroid 

 to the arytenoids, and by moving these latter cartilages they can be 



