384 
EDWARD PHELPS ALLIS. 
segments early in development, and its walls develop into the 
intermandibularis and interhyoideus, which are at first con- 
tinuous with the mandibular and hyoid myotonies. The 
lower ends of the branchial myotomes separate from the wall 
of the branchial portion of the cephalic coelom, and they 
develop into the branchial muscles. No muscles are directly 
formed from the wall of the branchial portion of the cephalic 
coelom, which subsequently retreats from the head.” This 
strikingly recalls van Wijhe’s description of the development 
of the coracobranchialis + coracomandibularis muscles in 
these same fishes, but it seems certain that the observations 
of these two authors do not relate to the same muscles. Of 
the intermandibularis of Scyllium Edgeworth says (loc. cit., 
p. 180) : “ The intermandibularis (Cs 2 of Vetter, C 2 mv of 
Ruge) is formed from the ventral portion of the mandibular 
cavity, which, as mentioned above, does not meet its fellow in 
the mid-ventral line, but passes backwards ventro- median to 
the ventral end of the hyoid cavity to open into the fore end 
of the cephalic coelom.” Here, in Scyllium, the inter- 
mandibularis is thus definitely said to arise from the 
mandibular cavit} 7 and hence not from a part of the cephalic 
coelom, which would seem to be in direct contradiction to the 
statement just previously made. Edgeworth then further 
says: “It results from this that there is no developmental 
stage in which the intermandibularis lies altogether in front 
of the interhyoideus. It gradually extends backwards, 
underlying the interhyoideus, so that in 23 mm. embryos its 
hinder end lies posterior to the ventral end of the cerato- 
hyal.” 
Luther (1909, p. 97) has already made brief reference to- 
this development of the intermandibularis and interhyoideus 
from parts of the cephalic coelom, as set forth in an earlier 
work of Edgeworth’s (1902) which I have not been able to- 
consult, and he, Luther, expresses much doubt as to its being 
correct, an opinion which I strongly share. My reasons for 
considering it incorrect can be best explained by reference to 
Scammon’s (1911) figures of the head somites in embryos of 
