The Amphibian larynx. 30& 



ventral half is directed anteriorly and the pharyngeal (dorsal) half 

 posteriorly. This rotation corresponds in direction to that observed 

 in the more specialized Anura, but an important difference to be ob- 

 served is that here the rotation afiects the musculature alone, while 

 in the Anura the cartilages take the initiative in the movement, the 

 muscles being aifected only in so far as they are connected with the 

 cartilages. According to Göppert the laryngeal ring of the Sala- 

 màndridae is a secondary formation and does not correspond to the 

 original Laryngei, but is composed of circular fibres derived from 

 these. To this element he has given the name "Sphincter laryn- 

 gis". The process by which this change occurs is well outlined by 

 him, and seems to consist of a growth or modification of the Laryngei 

 rather than the formation of a new muscle. In Siren, however, or 

 even in JSecturus, the first and last sections of a transverse series 

 show continuous fibres, of a lenticular or circular outline, entirely 

 enclosing the arytaenoids and acting as a sphincter (see sections of 

 Siren in No. 11) and on the other hand a section through the larynx 

 of an adult Triton, taken higher up than in Göppert's fig. 5 (No. 6), 

 as, for example, in fig. 6 of the same article, will show as complete 

 an interruption of the ring laterally as in the case of the lower forms. 

 In fig. 6 the fragment interpreted by Göppert as the disappear- 

 ing rudiment of the Laryugeus dorsalis may be merely a portion ol^ 

 the ring muscle, cut in this way because of the obliquity of the plane 

 of the ring to the plane of section. On these accounts and others 

 presented farther on v. sub Bactylethra. I hardly feel like con- 

 sidering the sphincter as more than a modification of the original 

 Laryngei, and of thus considering the laryngeal ring of Triton as 

 essentially difïerent from that of Siren or of Necturus. 



E, The laryngeal muscles of the Anura. 



a) The laryngeal muscles in Rana ; their development 



and adult anatomy. 



There appear to be no Anura which in their adult anatomy, pre- 

 sent transitional forms from Urodeles, but on the other hand in pro- 

 portion as the Anuran type is distinct, it is also uniform. I have 

 taken Rana clamitans as the type for the Anuran laryngeal anatomy, 

 and have augmented the study of the adult form by sets of serial 

 sections taken from various larval stages. 



Frog tadpoles attain nearly their full size before their limbs 



