JIOKPHOLOGY OF CRANIAL MUSCLES IX SOME YERTEBRxVi'ES. 289 



Graham Kerr's opinion was that "the Teleostoines the 

 Dipnoans and the Amphibians have arisen in phylog-eny from 

 a common stem 



Kellicott's statements that " the resembhmces in the 

 vascular system between Ceratodus (the most primitive of the 

 hving Dipnoi) and the Amphibia, especially Urodela, are 

 numerous and fundamental and cannot bo explained as 

 parallelisms/' and that ''most of the Elasmobranch 

 characters are parallelisms, some of them actually being 

 preceded by Amphibian conditions (e.g. the carotid arteries) " 

 are also true of the cranial muscles. 



Consideration of the common features in the cranial 

 muscles of Teleostoman embryos leads to the probability that 

 some remote ancestors possessed — a mandibular myotome 

 divided into upper and lower parts ^ ; a levator hyoidei, which, 

 owing to the upgrowth of the liyoid bar to the periotic 

 capsule, was insei-ted into the inner or posterior surface of a 

 hyomandibula ; a dorso-venti-al sheet in the opercular fold, 

 divided into a M. opercularis and a constrictor operculi ; a 

 series of levatores arcuum branchialium; a trapezius developed 

 from the fourth levator ; a series of Mm. marginales not fused 

 with the transversi ventrales; a series of hypobranchial- 

 cranial muscles consisting of interarcuales ventrales and of a 

 coraco-branchialis attached to the last branchial bar; 

 hypobranchial-spinal muscles, consisting" of a coraco-hyoideus, 

 and of a genio-hyoid, the hind end of which had grown back 

 to some more posterior branchial bar overlapping the coraco- 

 hyoideus. 



All these features, with five exceptions, may be supposed 

 to have characterised primitive Amphibia ; and these excep- 

 tions, viz. division of the mandibukir myotome, formation of 

 a M. opercularis, aud of a coraco-branchialis, backward 

 growth of the genio-hyoid, upward extension of the hyoid 



' On the supposition that the protractor hyonicindibuliiris of Aci- 

 penser is a case of atavism in its non-division into levator arcus 

 palatius and dilatator operculi, this division of the levator maxillae 

 suj)erioris would have once characterised the whole group. 



