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F. H. EDGEWORTH 



plate, and that the Levatores arcuum are separated from their 

 upper ends. 



In the case of the fifth branchial arch Greil stated that the 

 mesoblast (i. e. myotome downgrowth) forms the Dorso- 

 pharyngeus. I find that the development is similar to, but not 

 identical with, that of the more anterior arches. In the 



Text-fig. 19. 



m pL.v 



11 mm. embryo (Text-fig. 10) there is a lateral plate, the ventral 

 end of which is continuous with the pericardial wall. In the 

 13-0 mm. embryo (Text-figs. 16, 17) the muscle-plate is formed ; 

 and its ventral end has separated from the pericardial wall 

 and grown inwards forming the Transversus ventralis v. In 

 the IGmm. embryo some few fibres of the muscle-plate are 

 attached to Ceratobranchial v., but the majority are continuous 

 with the Transversus as in the 13-5 embryo. The condition is 

 a more primitive one than in other arches. The upper part 

 might be called a Levator or a Constrictor branchialis. The 



