382 



A Y'ERS. 



[Vol. VIII. 



being absent), are kept constantly open. The two remaining 

 cartilages form the pair of relatively large arytenoids. They 

 fill in the opening of the cricoid ring and project dorsad in the 

 form of an elliptical cupola, whose upper surface may be seen 

 forming the glottidian eminence in the floor of the Frog's 

 mouth. Within this dome the vocal cords are stretched in such 

 fashion that the slit between them lies directly over and 

 parallel with the median plate formed by the coalesced walls of 



Cut I. — A dorsal view of the Frog's larynx dissected to show the cartilages and 

 muscles. By., Hyoid Cartilage; C.I., CaL, Cp.l., Constrictors; Z>./., Dilator. 



the adjacent lung roots (the equivalent of the carina of human- 

 anatomy.) 



To this cartilaginous skeleton are attatched three pairs of 

 muscles. A dilator laryngis and two pairs of constrictors. 

 These muscles are all very nearly the same in mass and, since it 

 contains two sets of muscles, the constrictor group is twice as 

 strong as the dilator group, and serves to keep the glottis 

 closed most of the time. Under certain conditions the dilators 

 contract and produce an opening of the glottis. It follows 

 from what is given in the table below that there is very 

 probably an elastic action of the cartilages of the rivta glottidis 

 which aid the muscles in maintaining the normal closure of the 

 glottis against the pressure of the air swallowed into the lungs 



