526 



F. H. EDGEWORTH, 



by the myotomes of Lacerta aud Gall us are closely similar to 

 those of Scyllium. 



Myotome of the Mandibular Segment. — Thesuperior 

 oblique muscle of Gallus is developed as a forward and 

 upward directed off-shoot of the upper end of the mandibular 

 myotome (text-fig. 8, p. 516), just as in Scyllium. It never 

 contains a lumen. In these respects it resembles the superior 

 oblique of Lacerta (Corning). In some Birds — Anas, Larus 

 (v. Wijhe), it has a transitory lumen — possibly owing to a 

 relatively earlier formation. 



g/oss 



gen hyaid 



Bhbp. 



— /ery.m an 



ant.my/o 



thyr. 



Text-fig. 20. — Sagittal section tlirougli an embryo of Clielone, 

 in " stage 4 " of Parker, (For explanation of lettering see p. 555.) 



In Scyllium the mandibular mj^otome (after separation of 

 the Anlage of the superior oblique) forms a vertical strip 

 lying across aud outside the horizontal palato-pterygoid 

 process of the quadrate. It divides into an upper part above 

 the palato-pterygoid process, aud a lower between this and 

 Meckel's cartilage — the upper part forming the levator 

 maxillee superioris, and the lower the adductor mandibulae. 

 A portion, however, of the strip does not so divide, and forms 

 the first dorsal constrictor. 



