VISCERAL ARCHKS OF THE GNATHOSTOME FISHES. 401 
The dorsal portiou of the constrictor of the ultimate 
branchial arch undergoes excessive development and becomes 
the musculus trapezius. 
In the Teleostomi, each branchial bar, although inclined to 
the axis of the body as in the Selachii, continues to lie, 
approximately, in a single plane, and the dorsal and ventral 
ends of the constrictores do not turn posteriorly as in the 
Selachii. The pull of the constrictor, when contracting, did 
not, accordingly, tend to make the muscle slip, in the middle 
of its length, over the anterior edge of the branchial bar of 
its arch, but in certain of the branchial arches of the G-anoidei 
the proximal edge of the muscle slipped over the posterior 
edge of the branchial bar, and there gave rise to an adductor 
that is the functional equivalent but not the homologue of 
the adductor of the Selachii. The remaining fibres of the 
middle portion of the constrictor either later aborted or, 
possibly, became modified to form the radially arranged 
muscles related to the supporting rods of the branchial 
filaments. The dorsal and ventral ends of the constrictores 
became the levatores and the transversi and obliqui dorsales 
and ventrales. The levator of the ultimate arch is a slender 
muscle, and may secondarily acquire insertion on the shoulder- 
girdle. It is the homologue of the large musculus trapezius 
of the Selachii. 
In the hyal arch of the Teleostomi, the constrictor persists 
to a greater extent than in the branchial arches. Its dorsal 
portion becomes the adductor hyomandibularis and the 
adductor and levator operculi, these muscles, together, being 
the equivalent of the levatores of the branchial arches of the 
Teleostomi and of the dorsal ends of the constrictores of the 
Selachii. 
The ventral portion of the constrictor of the ultimate, or 
fifth, branchial arch of the Teleostomi is modified to form 
the musculi coracobranchiales or pharyngoclaviculares, these 
muscles of these fishes thus being branchial muscles, and 
hence probably not the homologues of the coracobranchiales 
of the Selachii. They always retain, in all fishes that I have 
