232 F. H. EDGEWOBTH. 



Branchial Mdscles. 



The homologies between the brauchial muscles of various 

 vertebrates are obscured by the nbsence of uniformity in 

 nomenclature. The word " interbranchial " has been applied 

 to many quite different muscles. It was used by Vetter to 

 denote the layer of muscle-fibres which lies external to the 

 branchial bars and internal to the supeificial constrictor in 

 Selachii. It was subsequently employed by Bronn and by 

 Schultze to denote longitudinal muscles between the ventral 

 ends of branchial bars in Amphibia; by Driiner, to denote 

 transverse muscles in Amphibia ; by K. Fiii'bringer and by 

 Greil to denote slender vertical muscles in Ceratodus. 



In this paper the word "interbranchial" is used exclusively 

 in the Selachii in the sense of Vetter; longitudinal muscles 

 between the ventral ends of branchial bars are called '' inter- 

 arcuales veutrales" (vide infra); tj-ansverse muscles are 

 called '^ transversi ventrales," and the vertical muscles of 

 Ceratodus are called Mm. marginales, as they ai-e exactly 

 homologons with the Mm. marginales of Anuian larvfe 

 described by Schultze. 



Fiirbringer included two sets of nmscles under the term 

 " hypobranchial spinal musculature"^ — (1) Those which are 

 sometimes called ventral longitudinal muscles, e.g. coraco- 

 mandibnlaris, coraco - hyoideus, genio - hj^oideus, sterno- 

 hyoideus ; (2) the coraco-branchiales of Elasmobranchs, 

 Teleostomi, and Dipnoi. 



Investigation of the development of these muscles, how- 

 ever, shows that whereas the ventral longitudinal muscles 

 are derived from trunk-myotomes, the coraco-branchiales 

 are derived from the ventral end of one or more branchial 

 myotomes, i.e. are of cranial origin. The above-mentioned 

 terminology would therefore appear to be in need of revision, 



' The name '" hypoglossal musculatiu-e " employed by Neal and by 

 Corning has nearly, but not quite, the same meiuiing as Fiirbringer's 

 " liypoljranchial spinal masculature," e.g., it would inclnde the cerato- 

 hyoideiis (interarcualis ventralis I) of Sphenodon. 



