346 F. H. EDGEWORTH 



arcualis rectus v. passing from the fiftli to the fourth Cerato- 

 branchial, and resemblmg the Subarcuahs rectus iv a of Urodela 

 in its forward extension to the first Ceratobranchial. I do not 

 know of any homologue of the Cleido-branchiahs in other groups. 



Transversi ventrales ii, iii, iv, v are present — 

 Greil stated that they are developed from the ventral ends of 

 the mesoderm, i. e. myotome downgrowth, in the second, third, 

 fourth, and fifth branchial arches by inward growth. I find that 

 they are developed by inward growth from the ventral ends of 

 the branchial muscle-plates (vide supra). I would add that 

 Transversus ventralis iv. is not always developed, possibly 

 owing to the relatively great size of Transversus ventralis v. 

 Greil held that the Subarcualis rectus i. s. Branchio-hyoideus, 

 developed in the first branchial arch, is serially homologous 

 with the Transversi ventrales of the hinder arches. But it is 

 difficult to think that a longitudinal muscle in one arch is 

 serially homologous with a transverse one in another when 

 neither changes its direction during development. In larvae 

 of Ichthyophis and Siphonops a Subarcualis rectus i. and 

 a Transversus ventralis i. are both developed in the first 

 branchial arch. In Ceratodus, too, a Subarcualis rectus and 

 a Transversus ventralis are developed in the fifth branchial 

 arch. Transversi ventrales iv. and v. occur in Lepidosiren and 

 Protopterus. The Subarcuales recti and Transversi ventrales 

 are homologous or serially homologous with those of Ganoids 

 and Amphibia. 



Transversus ventralis v. and Sphincter oeso- 

 phagi et laryngis. — The Transversus ventralis v., as stated 

 above, is developed in a 13-5 mm. embryo, as an inward 

 growth from the ventral end of the fifth branchial muscle- 

 plate (Text-figs. 16, 17). It extends back behind the posterior 

 edge of the sixth gill-clefts to a greater degree laterally than in 

 the median line, the distances being 96 [x and 40 ju. i. e. the pos- 

 terior edge of the muscle is concave from side to side. The 

 muscle in subsequent stages spreads backwards below the 

 anterior part of the oesophagus (Text-figs. 21-4). This is 

 concurrent with a backward shifting of the larynx (vide infra), 



