VISCERAL ARCHES OP THE GNATHOSTOME FISHES. 323 
and being firmly attached to the external surface of the 
dorsal trunk muscles, and as the line separating the dorsal 
and ventral trunk muscles here lies considerably ventral to 
the latero-sensory canal, and hence ventral to the dor>al 
edge of the trapezius, the fascia lies internal to the latter 
muscle as well as to the latero-sensory canal. Vetter says 
that this fascia lies upon the external surface of the musculus 
trapezius, and he so shows it in his figure of Heptanchus. 
Tt lies internal to that muscle in my specimens of Scyllium. 
There are however, in Scyllium, delicate tendinous lines 
which lie on the external surface of the trapezius and extend 
from the dorsal edge of the several constrictores to the tissues 
that surround the latero-sensory canal, and they apparently 
represent the tendinous bands (Platten) described and shown 
by Vetter. 
The dorsal edges of the branchial ■ constrictores are all 
irregular, the most dorsal point of each constrictor lying 
proximal (anterior) to the distal (posterior) edge of the 
muscle. From this most dorsal point the dorsal edge of 
each muscle descends anteriorly, crossing the external surface 
of the trapezius, and, in the anterior arches, extending 
ventro-anteriorly beyond the antero-ventral edge of that 
muscle. Where they cross the trapezius the dorsal edges of 
these constrictores are inserted on, or firmly attached to, that 
muscle, certain of the tendinous ends of the muscles pene- 
trating the trapezius. The distal fibres of each constrictor 
are inserted, as already stated, on the external (anterior) 
surface of the next posterior constrictor. The distal (posterior) 
fibres of the fourth branchial constrictor cross the external 
surface of the shoulder-girdle, and are inserted on the anterior 
edge of that cartilage along with the fibres of the musculus 
trapezius. 
The dorsal portion of the apparently continuous muscle- 
sheet that is exposed when the dermis is removed is thus not 
at all a continuous sheet, and the dorsal edge of the sheet, 
excepting in its hyal portion, is formed by the dorsal ends of 
those muscle-strands, only, that lie in the distal portion of 
