226 F. H. EDGEWOETH. 



to Meckel's cartilage, foniiing the depressor maiidibuk^. In 

 Raiia this also occurs at metamorphosis, the muscle forming- 

 the outer part of the depressor raandibulas. In Scyllium the 

 levator hyoidei, on the upgrowth of the hyoid bar, is inserted 

 into its outer surface, and in very late stages of development 

 extends forwards to the quadrate. In Teleostomi, on the up- 

 oTowth of the hyoid bar, the levator hyoidei becomes inserted 

 into its posterior edge or inner surface, and in Sahno 

 additionally spreads forward to the palato-quadrate. In 

 Ceratodus the insertion of the levator hyoidei to the upper 

 end of the ceratohyal is lost, but it is preserved in Protopterus 

 (vide description by Ruge). In Lepus there is no stage in 

 development in which there is a levator hyoidei inserted into 

 the upper end of a hyoid bar, for this is formed simultaneousl}^ 

 in its whole length, but the portion of the myotome above the 

 Anlage of the hyo-maxillaris (anterior digastric) is a mass, 

 which is homologous with the levator hyoidei of other forms, 

 and lies outside the hyoid bar ; it subsequently divides into 

 stapedius, stylohyoideus and digastricus posterior. It is 

 homologous with the M. styloideus of Monotremes. The 

 upper end of the levator hyoidei is attached to the auditory 

 capsule ; this attachment, in Anura, is preceded by a larval 

 stao-e, in which the upper end ol the muscle takes origin 

 from the processus muscularis of the palato-quadrate bar. 



The prinuiry form of the interhyoideus — formed from the 

 walls of the obliterated hyoid section of the cephalic coelom, 

 and serially homologous with the intermandibularis — wouki 

 appear to have been a transverse band connecting the two 

 hyoid bars, but in all forms examined, other than Rana and 

 Alytes, it extends backwards. In Urodela, Anura, and 

 rabbit there is a backward extension of the interhyoideus 

 only, but in Selachii, Teleostomi, Ceratodus, and Sauropsida, 

 of both myotome and interhyoideus, forming a continuous 

 ventro-dorsal sheet (Covd of Ruge) behind the hyoid bar. 

 Tlie l^ackward extension of the interhyoideus. or of this and 

 of the myotome, takes place in the opercular fold in Urodela, 

 Anura, Ceratodus, and Teleostomi; in part in the opercular 



