198 



F. H. EDGE WORTH. 



correlative of an undivided mandibulai* myotome, to form a 

 point d'appui for tlie lower jaw. 



It would follow that the streptostylic condition present in 

 Selachians, Teleostotni, and Sauropsidan embryos is one 

 which developed in correlation with a division of the myotome 

 into upper and lower parts, inserted into and arising from 

 the palatine process of the quadrate. 



Text-fig. 24. 



Utt.Sujj. 





\MXk^n\.OMA, 



24. 



Lepiclosteus, embi-yo 12 umi., transverse section. 



In Ceratodus, Ampliibia, and Lepus, where the mandi- 

 bular myotome does not become divided into upper and lower 

 parts, it separates into internal and external portions. In the 

 Anuran larvas the outer division divides into parts, some of 

 which have a temporary insertion into the superior lal)ial 

 cartilage, and the whole myotome assumes a nearly hori- 

 zontal position in correlation with that of the palato-quadrate 

 bar; at metamorphosis both bar and muscles rotate into a 

 more vertical position. In the rabbit the inner division sepa- 

 rates into the internal pterygoid and the tensor tympani 



