EDWAKD PHELPS ALLIS. 
314 
adductor muscle is much smaller than the incisure in the 
edge of the constrictor. 
The innermost (proximal) fibres of the dorsal portions of 
the constrictores are said by Vetter to have their origins on 
the inner ends of the “ ausseren Kiemenbogen,” that is, on 
the dorsal extrabranchials. It is not said to which arch the 
extrabranchial related to each muscle belongs, but the use 
of the expression “ ausseren Kiemenbogen,” without qualifica- 
tion, and the fact that there is no extrabranchial in the arch 
posterior to the posterior constrictor (Fiirbringer, 1903, p. 432), 
leads me to conclude that this origin of these fibres of each con- 
strictor is on the dorsal extrabranchial of the arch to which 
the constrictor belongs. In Heptanchus, the outer (distal) 
halves of the dorsal extrabranchials are said, in a footnote 
(loc. cit., p. 409), to be almost completely imbedded in the 
fibres of the constrictores, and on a later page (loc. cit., p. 
429) it is said that : “ Die sehr schwach ausgebildeten dorsalen 
wie ventralen ausseren Kiemenbogen liegen, z. Th. in die 
Muskeln selbst eingebettet, nahe deren obern und untern 
Enden auf denselben.” This statement that the extrabranchials 
lie “ on ” the constrictores is markedly indefinite, but as they 
usually lie against the posterior surface of the constrictor of 
the arch to which they themselves belong, and as Vetter says 
that all of the branchial rays of this fish have that position, 
one at first concludes that that must also be the position of 
the extrabranchials. But in one of Vetter’s figures (loc. 
cit., fig 1, PI. 14), six of these extrabranchials are shown 
lying one on the anterior surface of each of the six con- 
strictores of the branchial arches, and apparently slightly 
imbedded in it. 
This unusual position of these extrabranchials is one of 
the points in Vetter’s description that I have never been able 
to comprehend, and as I have two considerably dissected 
heads of Heptanchus I have examined them with reference 
to this. In each of these heads the outer (distal) end of the 
dorsal extrabranchial of each branchial arch lies posterior 
(internal) to the constrictor of the related arch, as it 
