312 H. H. WILDER, 



sider then, that here is introduced an entirely new muscular element, 

 characterised by an extremely long tendon. 



It arises in Hyla as a separate pair, each element from the 

 posterior inner angle of the arytaenoids, but in Acris the two elements 

 of the pair are united at their origin and superficially attached to the 

 arytaenoids. In both cases the muscles expand into fusiform bellies, 

 and are continued as narrow tendons up over the convex surfaces of 

 the arytaenoids and are inserted into the anterior inner angles of the 

 same cartilages. 



By considering their origin and insertion their action may be 

 readily seen to result in lessening the curvature of the arytaenoid 

 cartilages, and, by increasing the distance between their anterior and 

 posterior terminations, to render tense the vocal chords which are 

 stretched between them. 



The action may be conceived of as being the same as that which 

 would be produced by bending back a supple tortoise shell, equipped 

 with strings stretched across its concave surface, after the manner of 

 a primitive lyre. The muscle may thus be termed the Tensor chor- 

 darum (/s), referring to its physiological action. After this conside- 

 ration of Acris^ we have no difficulty in understanding the two figures 

 of Hyln (Figs. 48—49). Dilatator and Constrictor appear as in Rana, 

 the latter beiog relieved of its connection with the Sphincter, by the 

 complete disappearance of the latter as such ^). This has plainly 

 been converted into the muscle called here the Constrictor laryngis 

 and partially homologous at least with the muscle of the same name 

 previously figured. Its insertion here into a wide aponeurotic tendon, 

 which is free from the arytaenoids, but inserted itself by two delicate 

 tendons into the body of the annulus, is unique (Fig. 49). 



Bomhinator, aberrant in every particular, seems to possess a 

 simple Sphincter, into whose raphes have grown the wide ventral and 

 dorsal piece of the annulus which assist in forming the resonance 

 box already described. The muscles thus become a layer of trans- 

 verse fibres, filling in the deep lateral notches of the resonance box 

 and completing its walls (Figs. 46 and 47). The sphincter in Dacty- 



1) This muscle contains a sesamoid, evidently a fused pair, in its 

 median tendon (see Fig. 50). This is plainly the same element seen in 

 Chorophilus where the Constrictor has not separated from the Sphincter. 

 Thus the raphe in the middle of the Constrictor is shown to be the 

 raphe of the original Sphincter, and furnishes a farther proof of the 

 identity of the Cocstrictor laryngis, with a portion of the laryngeal ring. 



