328 
EDWARD PHELPS ALLIS. 
hyal arch the entire ventral end of the constrictor lies 
anterior even to the coracornandibnlaris. 
Most of the muscle strands of each constrictor lie every- 
where anterior (external) to the extrabranchial and branchial 
rays of their arch, but a few of them are, as above described, 
inserted on the dorsal and ventral extrabranchials. An 
angular piece has been cut out of the proximal edge of the 
primitive constrictor by the articulating ends of the epi- 
branchial and ceratobranchial of the arch, and the cut ends 
of the muscle fibres are inserted on those cartilages ; the 
angular piece so cut out forming the adductor of the arch, and 
the dorsal portions of the cut fibres becoming the musculus 
arcualis dorsalis. 
The gill-pouches, with their enclosed branchial lamellae, 
are thick, cushion-shaped structures. The external opening 
of the pouch lies, in a state of repose, at the outer edge of 
the posterior wall of the pouch, and it is smaller than the 
interna], pharyngeal opening of the pouch. The dorsal and 
ventral edges of the pouch are convex, the greatest height of 
the pouch being in the line of the outer ends of the branchial 
lamellae and not at the pharyngeal opening of the pouch. 
The anterior wall of the pouch curves posteriorly over the 
distal ends of the branchial lamellae, and the branchial rays, 
lying against the anterior (external) surface of that wall, are 
similarly curved at their outer (distal) ends. The constrictor 
that lies anterior to a gill-pouch lies on the anterior surface 
of these branchial rays, and, following the curve in the rays, 
curves posteriorly over them, the distal portion of the muscle 
lying in the plane of the external surface of the body, and 
the proximal portion lying in a plane directed antero-mesially 
at an angle of about 45° to that surface. The hyal con- 
strictor is not so curved, there being no gill-pouch anterior 
to it and the cartilaginous bar of the arch lying nearer the 
external surface than do the bars of the branchial arches. 
The posterior wall of each gill-pouch presses against the 
anterior surface of the constrictor next posterior to it, and 
forms a slight depression on that surface. The outer edge 
