MORPHOLOGY OF CRANIAL MUSOLES IN SOME VERTEBRATES. 179 



develop into the branchial muscles. No muscles are directly 

 formed from the walls of the branchial portion of the cephalic' 

 coelom, which subsequently retreats from the head. 



Mandibular Muscles. 



ScylHum. — On the formation of the palato-quadrate, in 

 16 mm. embryos, the mandibular myotome lies outside of and 

 across the palatine process, and then separates into an upper 



Text-fig. 7. 



— ^cuiJl raaj\^. 



Scylliuui. embryo 17 mm., transverse section. The right side of 

 tlie section is slightly anterior to the left. 



levator maxilUe superioris and lower adductor mandibuljB, 

 the process beginning in 20 mm. embryos (Text-fig. 11). The 

 separation of these two muscles by the palato-quadrate is com- 

 plete, and this is also the case in Acanthias, where, acccord- 

 ing to Marion, the hinder portion of the levator maxillaB superi- 

 oris — forming a separate first dorsal constrictor — is inserted 

 into the lower jaw. This must consequently be the result of 

 secondary downgrowth. The upper edge of the adductor 

 mandibulte gains, anteriorly, an additional origin from the 

 suborbital cartilage in 30 mm. embryos (Text-fig. 17), and 

 this anterior portion of the adductor separates, in 40 mm. 



