306 H. H. WILDER, 



appear externally. The fore-limbs are first in develoi)ment but are 

 hidden beneath the larval skin until the hind-limbs have attained con- 

 siderable size. The fore-limbs make their appearance externally by 

 breaking through the larval skin which then fits for a time about the 

 shoulders as the arm-holes of a vest about the arm. It is at this 

 period that the tail begins to absorb, and the adult form is rapidly 

 reached through gradual reduction of the tail, growth of the limbs, 

 and modification of the shape of head and body. My investigations 

 of the development of the larynx have extended through all these 

 periods, beginning at full-grown tadpoles with rudiments of hind- 

 limb, and concluding with well-formed frogs bearing a caudal stump 

 of 2 — 3 mm. At this stage the larynx is practically in the adult 

 condition. 



At the first stage investigated (tadpoles with rudiments of hind- 

 limbs), there exists a single pair of laryngeal cartilages, the arytae- 

 noids, surrounded by a complete ring-muscle, the Sphincter 

 laryngis of Göppert, traversed by median dorsal and ventral raphes. 



The plane of this ring is somewhat elevated vent rally as in 

 Triton. In addition to this a pair of narrow band like muscles come 

 transversely across the neck from the dorsal region and are inserted 

 by tendons into the arytaenoidS; near their tips, the tendons passing 

 entirely above (anterior to) the ring. By a comparison with Urodeles, 

 this stage is seen to strikingly resemble Triton, the sjthiucter being 

 similar, and the long transverse muscle identical with the D o r s o - 

 laryngeus (D^); a Digastricus pharyngis (Dg -f- FJ, or any muscular 

 element corresponding to the 6^'' visceral arch, appears to fail ^). 



The diagram of the 7'^ visceral arch and its muscles, in the lower 

 part of Fig. D, would serve to represent this condition. There are 

 thus in the larval frog-larynx, two primary elements from which all 

 the adult laryngeal muscles are derived, the ring(FJ and the trans- 

 verse band (J)^). These elements may be taken in order, and their 

 derivatives given. 



1) It is probable that this element may appear in a younger stage 

 and afterwards disappear. Göppert indeed describes a "Hyo-pharyn- 

 geus" (Fg) in a larva of 11 mm but his conclusion that it gives rise 

 to the "H y - p h a r y n g e u s " of the adult (= Constrictor aditus 

 laryngis) is certainly erroneus, since this latter muscle is a direct 

 derivative of the laryngeal ring (V. infra). 



