On the Development of the Hypobranchial, 

 Branchial, and Laryngeal Muscles of Cera- 

 todus. With a Note on the Development of 

 the Quadrate and Epihyal. 



By 

 F. H. Edgeworth, M.D. 



With 39 Text-figures. 



As is well known, Wiedersheim stated that laryngeal muscles 

 exist in Lepidosiren and Protopterus, but are absent in Cera- 

 todus. He admitted, however, that the specimen investigated 

 was badly preserved. 



In a recently published paper (1920) on the laryngeal muscles 

 of Amphibia, I suggested that, possibly, they might be found 

 in better specimens. Owing to the skill and perseverance of 

 Dr. Bancroft I have come into possession of some well-preserved 

 heads, and also of a series of embryos up to the stage of 30 mm. 

 in length for purposes of investigation. The material also 

 enabled me to examine the development of the hypobranchial 

 and pharyngeal muscles, which, together with other structures, 

 have been the subject of an elaborate memoir by Greil. 

 In the description given by Semon of the development of 

 Ceratodus the embryos were depicted in a series of stages 

 numbered from 1 to 48, the last mentioned and oldest stage 

 described being an embryo of 17-8 mm. Greil's description is 

 based on Semon's stages, and also extended to stage 48. The 

 embryos described in this paper had been fixed in formalin, 

 and their lengths are given in millimetres. Their relation 

 to Semon's stages will be found in an appendix. 



NO. 267 z 



