VISCERAL ARCHES OF THE GNATHOSTOME FISHES. 327 
of the branchial arches. In the first branchial arch they 
pass internal (dorsal) to the musculus coracohyoideus, between 
it and the coracobranchialis I, and end, without reaching the 
median line, attached to the muscles between which they lie. 
They pass across the anterior edge of the ventral extra- 
branchial of their arch at the point where that extrabranchial 
bends posteriorly around the ventral edge of the next 
posterior gill-pouch, and they are twisted upon themselves so 
that their internal surface is presented externally. In the 
second branchial arch these fibres form a flat band which 
passes between the coracobranchiales I and II, and reaches 
the median line. There it is inserted, with its fellow of the 
opposite side, in a median aponeurosis which passes dorsally 
between the coracobranchiales II of opposite sides and is 
continuous with connective tissues that surround the truncus 
arteriosus and the pericardial chamber. In the third branchial 
arch the fibres separate into two bundles, one of which passes 
between the coracobranchiales I and II, and the other between 
the coracobranchiales II and III. The first bundle does not 
reach the median line, but the second and larg-er one reaches 
that line and is attached, with its fellow of the opposite side, 
to connective tissues that are attached to the tissues surround- 
ing the truncus arteriosus and pericardial chamber. Certain 
of those fibres of this muscle that are inserted on the ventral 
extrabranchial of their arch pass, with that extrabranchial, 
between the coracobranchiales III and IY ; the ventral end 
of this muscle thus being separated into three parts. In the 
fourth arch the fibres here under consideration form a flat 
band which passes dorsal to the coracobranchialis IY and is 
inserted on the lateral wall of the pericardial chamber, these 
fibres thus having the relation to the coracobranchiales that 
the extrabranchial of the arch would have if it were present. 
The proximal fibres of a constrictor thus tend to acquire a 
position anterior to the coracobranchialis that is assigned, by 
nomenclature, to its arch, the extrabranchial of the arch 
lying posterior to that coracobranchialis. This tendency is 
the more pronounced the more anterior the arch, and in the 
