334 F. H. EDGEWORTH 



Greil stated that the Coraco-hyoideus is innervated by the 

 N. hypobranchiahs (derived from Ni. occips. x, y, z, or y, z) 

 and by the R. hypobranchiahs of N. occipito-spin. a, whilst 

 the Genio-coracoideus is innervated by the E. hypohyoideus 

 of N. posttrematicus ix. He did not refer to Furbringer's 

 statement. 



I find in a 27 mm. embryo that an anterior branch of the 

 N. hypobranchiahs enters the posterior end of the Genio- 

 coracoideus, and have not found any branch of the IXth nerve 

 entering the muscle. 



The Genio-coracoideus and Coraco-hyoideus of Ceratodus 

 are homologous with the Genio-thoracicus and Coraco-hyoideus 

 of Protopterus and Lepidosiren. Agar has shown that the latter 

 is developed from myotomes x, y, z ; but did not describe the 

 development of the Genio-thoracicus. 



The Genio-coracoideus of Ceratodus resembles the Genio- 

 coracoideus s. Coraco-mandibularis of Selachii and the Genio- 

 branchialis s. Branchio-mandibularis of Ganoids in that it is 

 formed from the anterior constituent of the hypobranchial 

 spinal muscles and subsequently grows backwards overlapping 

 the posterior constituent — Coraco-hyoideus. 



On the Source of the Branchial Muscles. — Greil 

 stated that in a 5-9 mm. embryo the mesoderm lateral to the 

 branchial region of the alimentary canal — between this and the 

 ectoderm — is continuous with the epithelium of the pericar- 

 dium, and is to be regarded as ' lateral-plate '. In 6-6 to 9-8 mm. 

 embryos these lateral plates degenerate into connective tissue, 

 and their place is taken by downgrowths from the first and 

 second myotomes. The cells of these downgrowths are distin- 

 guishable from those of the lateral plates by the shape of their 

 nuclei and the later absorption of their yolk-granules. Pro- 

 cesses from the first myotomes penetrate the first three branchial 

 arches, whilst one from the second myotome forks over the 

 sixth gill-cleft into the fourth and fifth arches. In a 10-2 mm. 

 embryo these downgrowths separate from the myotomes above 

 and become the source of the branchial musculature. 



I find that in an embryo of 9-5 mm. (Text-figs. 1-5) the cell- 



