On the Development of the Hypobranchial, Branchial, and Laryngeal Muscles of Ceratodus. With a Note on the Development of the Quadrate and Epihyal

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Abstract
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. A tabular statement of the synonyms of the names employed has also been appended.

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