368 
EDWARD PHELPS ALLIS. 
Edgeworth comes to totally different conclusions regarding 
the primitive condition and the later differentiations of these 
muscles. He says (He. p. 259) : “The probable primitive 
condition of each of the branchial myotomes was, from above 
downwards, a levator, a marginalis, an interarcualis ventralis, 
and (the lateral half of) a tranversus ventralis,” which would 
seem to imply that there was, in this primitive condition as 
conceived by him, no simple continuous constrictor extending 
the full length of the arch. The interarcuales ventrales are 
said by him to be muscles that extend between the ventral 
ends of the branchial bars. The marginales are said (l.c_ 
p. 233) to be muscles found by Schultze in anuran larvae and 
having their exact liomologues in what Edgeworth calls the 
vertical muscles of Ceratodus. These vertical muscles of 
Ceratodus are called by both Fiirbringer (1904) and G-reil 
(1913) the interbranchiales, and they are said by Fiirbringer 
to extend from the neurocranium to a process on the ventral 
end of the ceratobranchial of the arch next anterior to the 
one to which the interbranchialis belongs. It would, 
accordingly seem as if these muscles must be remnants of 
the primitive constrictor of the arch and not interbranchiales;. 
and yet Edgeworth intercalates them, in each branchial arch 
of the primitive vertebrate, between the musculi levator and' 
interarcualis ventralis of that arch. Edgeworth (l.c. p. 178) 
considers the branchial muscles in the Amphibia to repre- 
sent the most primitive condition found in any vertebrate, and 
he (l.c. p. 176) furthermore thinks it probable that there 
were, in the primitive vertebrate, but two branchial arches, and 
that where other arches are now found they have been, 
subsequently added posterior to those two. 
Hyal Arch. 
Dohrn (1885) says that, in the hyal arch of selachians 
(Plagiostomi), that proximal portion of the myotome (Muscu- 
latur) out of which, in the branchial arches, the adductor is 
developed is wanting, its formation having been wholly pre- 
