VISCERAL AKCHES OF i HE GNATHOSTOME FISHES. 307 
part of the distal portion of the myotome that lies between 
these dorsal and ventral bends the musculus interbranch ial is 
is said to be developed. The musculus interbranchialis, as 
thus defined by Dohrn, is accordingdy that part of the distal 
portion of the continuous myotome that lies in, and extends 
the full length of, the related branchial diaphragm, that 
diaphragm being limited dorsally and ventrally by the dorsal 
and ventral edges of two adjoining gill-pouches. The inter- 
branchialis of the adult Selachii, as defined by Vetter, lies 
between the dorsal and ventral extrabranchials of the related 
arch, and the distal ends of these extrabranchials lie, respec- 
tively, ventral and dorsal to the dorsal and ventral edges of 
the next posterior gill-pouch, as will be later fully described, 
and as is imperfectly shown in Dohrn’s figures 1-4, PL 7. 
The interbranchialis of embryos, as defined by Dohrn, is 
accordingly not the same thing as the one defined by Vetter 
in the adult. The difference is, in fact, morphologically 
quite important, although it seems not to have been noticed 
by Dohrn. 
From the distal portion of that part of the myotome that 
lies dorsal to the dorsal bend in the myotome, Dohrn says 
(loc. cit. p. 113) that the musculus constrictor superficialis is 
developed. What is developed from the distal portion of that 
part of the myotome that lies ventral to the ventral bend is 
not clearly stated. Dohrn says (loc. cit. p. 114) : “Wie an 
der dorsalen Seite schlagt sich auch an der ventralen die 
proximale Portion des Muskelschlauches um die Fortsetzu ng 
des Knorpelbogens herum und bildet die tiefen Portionen des 
Musculus constrictor superficialis (Vetter) ; diesen Namen 
verdienen sie freilich nur cum grano salis, denn der Constrictor 
superficialis sollte nur aus denjenigen Muskeln bestehen^ 
welche von den distalen Portionen der urspriinglichen 
Muskelschlauche abstammen. In der That siud diese Muskeln 
auch vorlianden, aber in der VettePschen Monographic falsch 
gedeutet worden. Er beschreibt sie als einen Theil der M. 
Coraoo-arcuales, unter dem Namen M. coraco-branchiales ; sie 
haben aber urspriinglich nichts gemein mit M, coraco- 
