322 
EDWARD PHELPS ALLIS. 
adjoining muscles are there distinctly evident, and there is 
no insertion, at any point, of one muscle on the next posterior 
one. Both dorsal and ventral to the gill openings there are, 
in each branchial arch, two or three long muscle strands 
which start from the internal surface of each constrictor, 
near the dorsal and ventral ends of the next posterior gill 
opening, and running respectively dorsally and ventrally, 
join the muscle strands of the next posterior contrictor. 
They can, however, easily be lifted off that muscle, and 
are accordingly not shown, as separate strands, in the 
figures. 
The fibres of the constrictores are everywhere grouped 
into bundles, which in most places form lamellar bands which 
occupy the entire thickness of the muscle. Where the muscles 
are thin these flat bands become simple rounded strands, and 
they can all be referred to, for convenience of description, 
as strands of the muscles. 
The dorsal edge of the hyal constrictor is nearly straight, 
and reaches, or lies slightly ventral to, the latero-sensory 
canal of the body. Its anterior half, approximately, lies 
anterior to the musculus trapezius and external to the 
anterior portion of the dorsal muscles of the trunk. Its 
posterior half lies external to the musculus trapezius, and, at 
its hind end, overlaps the constrictor of the first branchial 
arch. The anterior portion of the muscle has its origin in 
part on the tissues that surround the latero-sensory canal, 
and in part, ventro-lateral to that canal, on a fascia that is 
evidently the dorsal superficial fascia of Vetter^s descriptions 
of Heptanchus, Acanthias, and Scymnus. The posterior 
portion of the muscle has its origin mostly on the external 
surfaces of the trapezius and the constrictor of the first 
branchial arch, certain of the tendinous ends of the fibres 
penetrating those muscles, but it has its origin also in part 
on ventral prolongations of the tissues that surround the 
latero-sensory canal of the body. The tissues that surround 
the latter canal lie directly upon and are firmly attached to 
the dorsal superficial fascia, that fascia lying directly upon 
