The Amphibian larynx. 311 



It may be that here rather less than half of the original spincter 

 has formed this muscle, and that consequently more than half is left 

 for the remaining muscle, which thus represents an element midway 

 between the complete Sphincter and the pharyngeal Compressor. 



I am uncertain concerning this, and wait for the decision to be 

 obtained from its development. 



Among the Hylidae, Chorophilus (Figs. 52 — 54) and Hylodes 

 (Fig. 56) present curiously primitive characteristics which may help 

 to explain the great complexity found among some of the other members 

 of the family. If we remove from Chorophilus the huge layer which 

 represents the Dilatator, there remains a simple muscular slip from 

 which anteriorly a delicate slip extends to near the distal end of the 

 thyroid process. The ring is plainly the Sphincter and the slip the 

 partially differentiated Constrictor, representing a stage in the onto- 

 geny of Rana and furnishing thus a beautiful anatomical corroboration 

 of the conclusions obtained from the development of Bana concerning 

 the origin of the Constrictor. Fig. 54 represents this isolated from 

 the rest. In no place does the Sphincter seem directly attached to 

 the arytaenoid cartilages but the dorsal and ventral raphes have 

 broadened out into tendons in which pairs of sesamoid cartilages have 

 developed. In Chorophilus I have proved by a, transverse series of 

 sections through the larynx of both sexes that the connection between 

 the Sphincter and the slip representing the Constrictor is one of com- 

 plete continuity. In the female Chorophilus (Fig. 53) the muscular 

 relations are the same as in the male, but excessively small. The 

 laryngeal anatomy of Acris gryllus (Fig. 51) stands intermediate be- 

 tween Chorophilus and Uyla^ and by means of this we are able to 

 suggest homologies which would be otherwise very obscure. 



Upon removing the Dilatator we may distinguish the ring-like 

 Sphincter and the slip-like Constrictor, still closely connected anteri- 

 orly, and differing from the same parts in Chorophilus mainly in their 

 relative proportions, the Constrictor having gained in size and the ring 

 being much attenuated. This attenuation of the ring receives a pos- 

 sible explanation in the presence of a new muscle outside of the ring 

 possessing below a large fleshy belly, and extending anteriorly into a 

 long and very narrow tendon. It is probable that this has separated 

 from the Sphincter much as in the case of the Compressor laryngis 

 of Bana and Bufo. That this is not the Compressor, however, is 

 sufficiently proven by the fact that in Hyla (Figs. 48 and 49) this 

 muscle exists side by side with a typical Compressor. We must con- 



