VISCERAL ARCHES OF THE GNATHOSTOME FISHES. 351 
adult Heptanchus is said by Vetter to arise mainly from the 
tendinous dorsal surface of the musculus coraeohyoideus ; the 
coracobranchiales of the second to the fifth arches to arise 
mainly from the dorsal surface of the musculus coracoarcualis 
communis, but in part from a tendinous cord formed in the 
mid-ventral line of a fascia that covers, ventrally, the peri- 
cardial chamber ; the sixth coracobranchialis to arise in part 
from the shoulder-girdle; and the seventh coracobranchialis 
to arise entirely from the shoulder-girdle. Running forward, 
these several muscles are all inserted mainly on the hypo- 
branchial of the arch to which they are assigned, but certain 
of the fibres of the muscle of the first arch are inserted on 
the basihyal, and certain of the fibres of the muscles of the 
second to the sixth arches, and all of the fibres of the muscle 
to the seventh arch, on the ceratobranchial of the corre- 
sponding arch. Although not so stated by Vetter, the 
coracobranchiales must, because of these origins and inser- 
tions, in a measure embrace the pericardial chamber, running 
at first dorso-laterally and then dorso-mesially around it. 
Deeper (proximal) and distal fibres of the ventral portions of 
the const rictores snperficiales both coexist with the several 
coracobranchiales. 
In Acanthias and Scymnus the coracobranchiales, as 
described by Vetter, seem to differ from those in Heptanchus 
mainly in that they arise ventrally, in Acanthias, from the 
outer edge of the fascia that covers the pericardial chamber 
-and in Scymnus from the shoulder-girdle and a process of 
the fifth ceratobranchial. Marion (1905) says that, in 
Acanthias, the coracobranchialis is composed of five parts and 
forms the lateral wall of the pericardial chamber. In both 
-Scy Ilium and Mustelus, as I have already fully described, 
musculi coracobranchiales coexist with both deeper (proximal) 
-and distal fibres of the constrictores superficiales, and there 
is every reason to believe that similar conditions are found in 
both Acanthias and Scymnus. 
In Chlamydoselachus I find the coracobranchiales of the 
third to the sixth branchial arches all arising, as a single 
