262 F. H. EDGEWORTH. 



A similar development of the laryngeal muscles takes 

 ])lace in Triton and in Rana. 



If the method of development of the lai'yng-eal muscles be 

 compared witli that of the branchial muscles it is seen that 

 they are very different. The branchial muscles are developed 

 from the branchial myotomes, the laryngeal muscles are 

 diffei'entiations of an oesophageal or pharyngeal constrictor, 

 Avhicli is formed from cells given off by the coelomic epi- 

 thelnm. In Polypterus and Ceratodus the larynx is 

 developed just behind the branchial region, in Amphibia in 

 the last, i.e. fourth branchial, segment. In Polypterus the 

 oesophageal constrictor is not attached to the trunk- 

 myotomes; in Ceratodus it is attached, though no dorso- 

 laryngei are developed ; in Amphibia dorso-laryngei are 

 developed. In Ceratodus there are no intrinsic lai'yngeal 

 muscles ; in Polypteriis there is a sphincter glottidis, which 

 remains in continuity with the constrictor of the oesophagus ; 

 in Amphibia there are laryngei or a sphincter lai'yngis, 

 which is not continuous with the constrictor of the pharynx. 

 In Polypterus and Ceratodus there are no skeletal structures ; 

 in Amphibia laryngeal cartilages are developed — later than 

 the branchial bars and ventral, not lateral to the pharynx. 

 These similarities and differences suggest that the conditions 

 found in l^olypterus and Ceratodus preserve stages in the 

 phylogenetic development of the laryngeal structures of 

 x\mphibia. They tend to confirm the theory of Wiedersheim. 

 The relations of the transversus ventralis of the last branchial 

 segment (fourth in Polypterus and Amphibia, fifth in Cera- 

 todus) to the laryngeal structures have been described above. 



In 5 mm. embryos of Chrysemys the opening of the larynx 

 is in the fourth branchial segment ; the coelomic epithelum in 

 the third and fourth branchial segments is thickened and 

 proliferating mesoblast cells, which surround the pharynx 

 and developing larynx. In 8 mm. embryos the opening of 

 the larynx is in the third and fourth branchial segments ; in 

 the fourth a constrictor pharyngis is formed from the 

 splanchnic mesoblast ; in the third and fourth the Anlagen of 



