MORPHOLOGY OF CRAXIAL MUSCLES IN SOME VEHTEBKATES. 297 



Thieren entwickelt welclie im Grade ihi-er Ausbildung 

 amphibienartigeTliiere g'leichzusetzen sind. . . ." Graham 

 Kerr's opinion was that "the ancestors of the Amniota 

 probably diverged about one or several points from the 

 region of the stem common to Dipnoi and Amphibia." 



As regards the cranial muscles, the differences between 



Text-fig. 9o. 



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95. 



Sauropsida and Amphibia have been mentioned above. In 

 the division of the mandibular myotome into upper and 

 lower portions, and in the formation of a ventro-dorsal sheet, 

 Covd, in the hyoid segment, Sauropsida resemble Selachii and 

 Teleostomi, and also as regards Covd, Dipnoi. The shifting 

 of insertion of the levator hyoidei from cerato-hyal to 

 Meckel's cartilage and the morphologically primitive con- 

 dition of the hypobranchial spinal muscles are common to 

 both Sauropsida and Amphibia. 



