210 F. H. EDGE WORTH. 



from the periotic capsule found. In Lepidosteus, Amia, and 

 Salmo, the Vllth nerve, at first winding round the hyoid 

 bar^ subsequently pierces the hyoniandibula owiug to chou- 

 drification spreading round it ; the more primitive condition 

 is preserved in Acipenser and Polypterus. 



The adult condition of the hyoid muscles in these Teleostomi 

 is not quite uniform. In all the dorso-ventral sheet Covd 

 divides into dorsal and ventral portions. In Polypterus the 

 anterior and posterior portions of the myotome do not separate 

 from each other, but form one muscle, the retractor hyomandi- 

 bularis et opercularis. In the others separation takes place ; 

 the anterior part, i.e. the original levator hyoidei, forms a 

 retractor hyomandibularis in Acipenser, and an adductor 

 hyomandibularis in Lepidosteus, Amia, and Salmo. The 

 posterior part, i. e. the upper part of C^vd, forms a M. 

 opercularis in Acipenser and Lepidosteus, an adductor and 

 levator operculi in Amia and Salmo. In 9i mm. embryos of 

 Salmo the adductor mandibularis additionally spreads forwards, 

 forming the adductor arcus palatini. 



The fore part of the interhyoideus of Acipenser forms the 

 hyoideus inferior (Cs- of Vetter), the hinder part, i.e. the 

 lower part of C^vd, forms a constrictor operculi (Csg and Cs^ 

 of Vetter). In Polypterus the condition is similar.^ In Lepi- 

 dosteus, Amia, and Salmo, the fore part forms the hyoideus 

 inferior; the hinder part becomes attached laterally to the 

 hyoid bar (only partially so in Lepidosteus), and forms the 

 hyoideus superioi*. The median raphe of these muscles is 

 preserved in Acipenser, Lepidosteus, and Polypterus; in 

 Salmo and Amia it is lost, and the hyoideus inferior becomes 

 attached to the hypohyals of the same and opposite side. 



In 8^ mm. embryos of Amia the Aulage of the hyomaxillaris" 

 muscle becomes separated fi-om the upper edge of the hyo- 

 hyoideus inferior (Text-fig. 29) ; it grows forward to Meckel's 



' luterniiixillaris posterior and mantle muscle of Pollard. 



■•^ Superior deeper portion of the geuio-hyoid of Allis. A different 

 terminology is used in tliis paper, as the word '"genio-liyoid"" is generally 

 used to denote the anterior element of the hypoljriinchial spinal muscles. 



