180 



F. H. EDGEWORTH. 



etiibryos, forming the levator labii superioris (or add. |3) of 

 Yetter. In 45 mm. embryos the add. 7 of Vetter is begin- 

 ning to be delaminated from the outer face of the adductor, 

 and the hindmost fibres of the adductor have grown down 

 into the intertnaudibularis, forming a band simihxr to that 

 described in Acantliias by Vetter. 



The intermaiidibularis (Csj of Vetter, CoUiv of Ruge) is 

 formed from the venti-al part of the mandibular cavity, 



Text-fig. 8. 



Ia-.OO.'I/ 



i'tA,.nxvj 



8. 



Scyllivim, embryo 17 mm., transverse section. 



whicli, as mentioned al)ove, does not meet its fellow in the 

 mid-ventriil line, but passes backwards ventro-median to the 

 ventral end of the liyoid cavity to open into the front end oi: 

 the cephalic coelom. It results from this that there is no 

 developmental stage in which the intermandibularis lies 

 altogether in front of the iiiterhyoideus. It gradually extends 

 backwards, underlying the intei'hyoideus, so that in 23 mm. 

 embryos its hinder edge lies posterior to the ventral ends of 

 the ceratohyals (Text-fig. 12). 



The nictating muscles of Scyllium (Ridewood) consist of a 

 levator palpebreB nictitantis, retractor palpebras superioris. 



