VISCERAL ARCHKS OF THE GNATHOSTOME FISHES. 315 
normally should. The outer ends of most of the branchial 
rays of each arch, however, pierce the constrictor of their 
arch, and from there onward lie against the anterior (external) 
surface of that constrictor, imbedded in that surface and 
covered by a thin sheet of connective tissue, which is strongly 
attached to the anterior (external) surface of the muscle on 
either side of the branchial ray. The muscle fibres pass 
unbroken beneath (posterior to) this end of the branchial 
ray, and none of them are inserted on it. There is no 
slightest indication that the fibres have been cut in two, 
and later grown together again. The conclusion is, there- 
fore, inevitable that these branchial rays, in growing outward, 
have pierced the constrictor, and so passed from its posterior 
(internal) to its anterior (external) surface ; and it seems 
probable that this is what happened with the extrabranchials 
in the specimen of this fish examined by Vetter. It is, 
however, singular that in my two specimens it should be 
the branchial rays that so pierce the muscle, and not the 
extrabranchials, while in Vetter’s specimen it was the extra- 
branchials, and not the branchial rays. Vetter’s figure is, 
in any event, misleading, if not actually incorrect, for no 
part of the constrictor of any of the branchial arches is 
shown lying anterior (external) to the related ex tr abranchial. 
A deeper (proximal) bundle of the ventral portion of each 
constrictor superficialis of Heptanchus is said by Vetter to 
have its ventral attachment, called by Vetter its origin, on 
a tendinous band related to the dorsal surface of the hypo- 
branchial muscles. Running dorsally from there, this bundle 
is said to either pass between two of the musculi coraco- 
branchiales of his description, or to perforate one of those 
muscles, and to be inserted on the ceratobranchial of its 
arch. This bundle of fibres might accordingly be considered 
to be a coracobranchialis, and Dohrn did actually so con- 
sider it. No musculus interbran chialis is differentiated in 
this fisli. 
In Acanthias, as in Heptanchus, the proximal (anterior) 
fibres of the constrictor superficialis of each branchial arch 
