320 
EDWARD PHELPS ALLIS. 
Acanthias, from a linear aponeurosis, called by Tiesing a 
septum, said to be formed between it and the corresponding 
muscle of the next posterior arch. Running antero-ventrally, 
the proximal (anterior) fibres are said to be inserted on the 
next anterior so-called septum, while the distal (posterior) 
fibres traverse the branchial diaphragm and are continuous 
with the fibres of the ventral constrictor superficialis. The 
ventral constrictor superficialis of each arch is said to arise 
from a median ventral superficial fascia, as in Heptanchus, 
and, running antero-dorsally, to be continuous with the distal 
fibres of the dorsal constrictor superficialis. No mention is 
made of any fibres not continuous with those distal fibres of 
the dorsal portion of the muscle, that large proximal portion 
of the ventral constrictor that is found in the Selachii 
described by Yetter thus not being accounted for in these 
descriptions of Mustelus. It is said that no ventral septum 
is found in this fish, Mustelus differing in this from Acanthias 
and resembling Heptanchus. Ruge says that the fibres of 
the ventral portions of the several constrictores all have a 
parallel course, and, their edges being contiguous and inti- 
mately bound to each other, form a single continuous muscle- 
sheet. 
The so-called septa of Mustelus are said by Tiesing (loc. 
cit., p. 100) to be formed by the “ Yerwachsung derKiemen- 
locher” between two adjoining arches, this agreeing with 
Vetter’s conclusion. Ruge (1897, p. 225) also says that these 
aponeuroses are found “an den Verwachsungsstellen tier 
freien Rander der Kiemen-Scheidewande.” Tiesing says of 
each septum that, “ nach innen und vorn zu befestigt es sieh 
an dem betreffenden Kiemenbogen and schliesst den oberen 
tiusseren Kiemenbogen ein.” But it is evidently impossible 
that a septum, formed where the outer edge of a branchial 
1 diaphragm has fused with the next posterior one, could be 
attached to the inner branchial bar of either of those two 
arches. Tiesing does not say to which arch the extrabran- 
chiaT related to a particular septum belongs, but Ruge says 
(loc. cit., p. 227) that the constrictor superficialis of the- 
