MOEPHOLOGY OF CKAXTAL MUSCLES IX SOIME VERTEBRATES. 199 



muscles, the outer division into the temporal, masseter, and 

 external pterygoid. 



Secondary changes take place in the levator maxillte 

 superioris and adductor mandibular in all the animals inves- 

 tigated : no one ^reserves them as such. In Scvllium the 



Text-fig. 2o. 



Ouxj-.ch 1 



VXCMtS v<^^.t 



Lepidosteus, embiyo 14 mm., transverse sectiun. 



Anlage of the nictating muscles is proliferated from tlie 

 levator maxillae superioris, and add. /3 and add. \ are sepa- 

 rated from the adductor. In Teleostomi the levator maxillae 

 supei'ioris either forms a protractor hyomandibularis or 

 divides into a dilatator operaculi and levator arcus palatini; 

 and the adductor may either remain single as in Salmo, or 

 divide into external and internal portions, of which either the 

 internal (Lepidosteus), or both (Amia, Polypterus), or ? the 



VOL. 56, PART 2. NEW SERIES. 15 



