544 



¥. H. EDGEWORTH. 



The Ventral Longitudinal Muscles are developed in 

 Scyllium from the five trunk-myotomes (4th to 8th), in Gallus 

 from the first five (text-fig. 9, p. 517), though the front part 

 of the first (of. text-fig. 2, p. 513) has by then disappeared ; in 

 Lacerta (Corning) from the second to the fifth, the first having 

 previously atrophied. Ventral downgrowths take place from 

 each contributing myotome in the form of a curve, with 

 concavity forwards, round the branchial region of the head. 

 The ventral ends of these downgrowths fuse togethei', sepa- 

 rate from the rest of the myotomes, and form an elongated 



fl.sup 





Text-fig. 39. — Sagittal section through an older emhrjo of 

 Tropidonotus. (For explanation of lettering see p. 555.) 



mass of cells in the ventral region of the branchial segments 

 dorsal to the cephalic portion of the ccelom. The mass 

 extends forwards and backwards to form the Anlage of the 

 ventral longitudinal muscles of the head and neck. 



In Scyllium it forms two parallel muscles — the coraco- 

 hyoideus and coraco-mandibularis. In the Sauropsida the 

 long column divides into ai; anterior and a posterior part — 

 the genio-hyoid and the sterno-hyoid. The division takes 

 place opposite the first branchial bar, and the primary condi- 

 tion of the genio-hyoid is that of a muscle passing from tlie 

 anterior end of Meckel's cartilage to the ventral end of the 



