MORPHOLOGY OF CEANIAL :\IUSCLES IN SOME VERTEBRATES. 287 



On the other hand^ the existence of a hyo-njaxillaris and of 

 Mm. niarginales, the insertion of the orbito-hyoideus or of 

 this and the suspensorio-hyoideus to the cerato-hyalj and the 

 origin of the trapezius from the skull, are primitive features 

 which are not developed or soon modified in Urodelau 

 development. 



In the Urodela the insertion of the levator hyoidei is 

 transferred, wholly or partially, from the hyoid bar to 

 Meckel's cartillage early in development, and the hyo- 

 maxillaris Anlage forms a ligament. The development of 

 gill-muscles from Anlagen which are homologous with those 

 which give rise to the Mm. margiuales of Anuran larv^ and 

 Ceratodus, and of a cerato-hyoideus externus, are features 

 peculiar to Urodela. 



Ceratodus resembles Selachii and some Teleostomi, and 

 differs from Amphibia in the backward growth of the genio- 

 hyoid to the shoulder-girdle, and in the formation of coraco- 

 branchiales. Ceratodus resembles Selachii aud Teleostoman 

 embryos, and differs from Amphibia in the backward growth 

 of both hyoid myotome and iuterhyoideus, resulting in the 

 formation of a continuous dorso-veutral sheet, C^vd, behind 

 the hyoid bar. Ceratodus resembles Teleostomi aud Amphi- 

 bia, and differs from Selachii in the formation of levatores 

 arcuum brauchialiuin aud in the development of the trapezius 

 from a levator. Ceratodus resembles Amphibia, and differs 

 from Selachii and Teleostomi in the non-division of the 

 mandibular myotome into upper and lower portions. Cera- 

 todus resembles Anuran larv« in the simple condition of the 

 Mm. margiuales, and Urodela in the ligamentous condition of 

 the hyo-maxillaris. 



According to K. Fiirbriuger, " Wenn wir somit keiue 

 bestimmte Ordnung der Amphibia von den Dipnoern 

 able i ten konneu, so ergiebt sich daraus kein Einwand 

 gegen eine Abstammung von den Dipnoern iiber- 



condition of the suctorial mouth and jaws in Aniu-an lai-vse was 



discussed hy Balfour and by Gaujap, though without reference to the 

 muscles. 



