348 
EDWARD PHELPS ALLIS. 
homologues of the so-called musculi interbranchialis pos- 
terior, interbranchialis anterior, and ceratohyoideus, which 
are developed, respectively, from the ventral ends of the 
axial mesoderm of the third, second, and first branchial 
arches, but lie anterior to, and hence morphologically ventral 
to, the truncus arteriosus. 
The superficial portion of the posteiior fork of the ventral 
process of the second trunk myotome grows ventrally 
external and ventral to the pericardial cavity, and appa- 
rently separates into three muscles, but there is some 
confusion in the name given to them. One of them is 
certainly the musculus clavicularis, or dorsoclavicularis, 
which, as above stated, is said by Greil to represent the 
phylogenetic beginning of a musculus trapezius (den ersten 
phyletischen Anfang eines Trapezius holier stehendenFormen). 
The second and third muscles are first called the dorso- 
branchinlis and dorsohypobranchialis, but later the names 
dorsobranchialis, dorsocleidobranchialis, coracocleidobran- 
chialis, cleidobranchialis, and coracobranchialis are appa- 
rently used either to designate those muscles themselves 
or muscles derived from them. 
The musculi dorsopharyngeus and dorsoclavicularis are 
definitely said by Greil (loc. cit., p. 1249) to be innervated by 
a branch of the nervus vagus given off close to the ramus 
intestinalis vagi. The other muscles derived from the ventral 
process of the second trunk myotome must then also, in 
embryos, be innervated by the vagus, but I do not find 
that this is so definitely stated. A muscle that Greil con- 
sidered to be the homologue of the trapezius is, in any 
event, said by him to be derived from the axial mesoderm 
of the fifth (or fifth and sixth) branchial arch, and it is 
innervated by a branch of the nervus vagus that has the 
position, serially considered, of a nerve of that arch (or 
arches) . 
Froriep (Greil, 1907, Discussion) thinks that this origin 
of the axial mesoderm of the fourth and fifth branchial 
arches of Ceratodus from a trunk myotome needs confirma- 
