MUSCLES OF CERATODUS 



337 



ziehenden axialen Mesoderms bildet, sondern durch Ziige spin- 

 deliger Zelleii, welche von der Dorsal- und Ventralseite 

 (Levatores und Interbranchiales) stammend, vorwachsen, 

 geschlossen wird '. This occurs in the description of the 

 17-8 mm. stage (p. 1355). No figures were given illustrating this 

 derivation of the Constrictors. 



In 10-5 and 12 mm. embryos, and as is additionally shown in 



Text-figs. 11-13. 

 Embryo 12 mm., sagittal sections ; Text-fig. 11 is the most external. 



Z branch, m pi 



LeroLtohyaL 



Text-figs. 11-13 taken from sagittal sections of a 12 mm. 

 embryo, the first and second branchial muscle-plates form 

 vertical strips through the whole extent of the arches. The 

 ventral end of the first branchial muscle-plate is detached from 

 the pericardial wall, and has grown a little forwards — towards, 

 but not yet reaching, the Ceratohyal. The ventral end of the 

 second branchial muscle-plate is continuous with the peri- 

 cardial' wall (Text-fig. 14). These muscle-plates, slightly 

 convex outwards, pass down external to the primordia of the 

 branchial bars. 



