346 
EDWARD PdELPS ALLIS. 
is said by Vetter to be innervated either by branches of the 
nervus intestinalis vagi, or, possibly, by that nerve together 
with delicate branches of other, more anterior portions of the 
vagus. In Prion odo n glaucus, that anterior bundle of 
the trapezius that has its insertion on the branchial bar of the 
ultimate arch of the fish is said by Vetter (1878, p. 460) to 
be innervated by a branch of the ri'ervus vagus quartus, the 
remainder of the muscle being innervated by the nervus 
intestinalis vagi. In Chlainydoselachus I find the muscle 
innervated by a branch of the vagus that lies next posterior to 
that branch of the nerve that is sent to the penultimate 
branchial arch. 
The anatomical evidence regarding this muscle in these 
several fishes, taken by itself, would thus evidently lead to 
the conclusion that the trapezius, in each of the fishes con- 
sidered, is simply a differentiation of the constrictor super- 
ficialis of the ultimate branchial arch of that particular fish — 
the seventh in Heptanclius, the sixth in Chlainydoselachus, 
and the fifth in Acanthias, Scynmus, and Mustelus — or, 
possibly, of that arch and other more posterior arches if such 
arches primarily existed and have successively disappeared 
by reduction or transformation. This conclusion would then 
differ from that arrived at by Vetter (1874, pp. 432-433) 
only in that the trapezius is considered to be derived mostly, 
or entirely, from the constrictor of the ultimate persisting 
branchial arch instead of from the constrictor of a modified 
and more posterior arch that is represented in the shoulder- 
girdle. This derivation of the muscle would also explain, and 
find confirmation in, DohriTs otherwise inexplicable failure to 
find it developed from the dorsal ends of all of the branchial 
myotonies, as Edgeworth maintains that it is developed; and 
the partial fusion of the proximal fibres of the dorsal portions 
of the constrictores superficiales of the second to the fourth 
branchial arches with the trapezius, in my specimens of 
Mustelus and Triakis, would probably explain how Edgeworth 
came to consider the latter muscle to be developed from the 
dorsal ends of all of the branchial myotonies. It is, however, 
