MOhTHUl/OGY OF (JEANIAL MUSCLES IN SOME VEKTEBlfATES. 223 



formed in Auiia and Salmo, but differs in that it is separated 

 from the upper end of the hyoideus inferior. The first men- 

 tioned method of formation is probably the primitive one, 

 for serially homologous muscles, interarcuales ventrales, are 

 formed from the lower ends of branchial myotomes where 

 there are no muscles homologous with the interhyoideus ; 

 the method of formation in these Teleostomi is probably 

 related to the secondary position of the adductor hyomandi- 

 bularis internal to the upper part of the hyoid bar. In 

 Urodela (Necturus, Triton), Ceratodus, Lepidosteus, and 



Text-fig. 50. 



Text-fig. 50. — Ceratodus, advanced embryo, length ? ; portion of 

 transverse section, to show relations of the liyoniandibular 

 cartilatre. 



Acipenser a corresponding Anlage develops into a hyo- 

 maxillaris ligament. In SeJachii (Seyllinm, Acanthias) and 

 in Sauropsida no hyo-maxillaris Anlage is formed. 



The developmental history of the hyo-maxillaiis suggests 

 that its primitive condition was tliat of a longitudinal muscle 

 passing from the hyoid bar to the hind end ot MeckeFs carti- 

 lage, but this is not preserved in an}' of the animals investi- 

 gated. In Teleostomi (Amia and Salmo) the front end of the 

 muscle extends forwards along Meckel's cartihige. 



In Chimsera there is a similar muscle (hyoideus inferior of 

 Vetter) extending from the hyoid bar along the lower jaw. 



