MORPHOLOGY OF CRANIAL MUSCLES IN SOME VERTEBRATES. 283 



mandibulo-liyo-brancliial skeleton to tlie shoulder-girdle, 

 and the change of function of the latter group of muscles to 

 one similar to that of the former tends to bring about a 

 secondary innervation from spinal nerves. 

 - A similar question arises in connection with the presence 

 and absence of levatores arcuum branchialium. It has been 

 suggested above that their absence and the related method 

 of formation of the trapezius are secondary phenomena 



Text-fig. 8^. 



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Rabbit, embryo 4: mux., longitudinal vertical section. 



84. 



(p. 257). If so, it is possible that this has been indepen- 

 dently acquired in Scyllium, Sauropsida, and rabbit. 



In Scyllium and the Teleostomi a stage of development 

 occurs in which there is a short hyoid bar like that of 

 Amphibia with a levator hyoidei, which is succeeded by one 

 in which the bar extends up to the periotic capsule. The 

 relationship of the muscles and of the facial nerve to the 

 later formed portion of the bar are so different in Scyllium 



