VISCERAL ARCHES OF THE GNATHOSTOME FISHES. 355 
branchial arches are said by Vetter (1878) to be repre- 
sented by special tendons of the musculus coracoarcualis 
anterior which are inserted, one each, on the hypobranchial 
of the corresponding arch, the main tendon of the muscle 
being inserted on the hypohyal. The coracobranchialis of 
the fourth arch is said to be probably wanting. The coraco- 
branchialis of the fifth arch is said to be represented by the 
single tendon of the coracoarcualis posterior, which tendon is 
inserted on a ligament which extends from the basibranchial 
of the fourth arch to the ventral end of the rudimentary 
branchial bar of the fifth arch. Furbringer (1897, p. 460) 
found the tendon of the latter muscle separated into two 
parts, one of which was inserted on the branchial bar of the 
fourth arch and the other on that bar of the fifth arch. 
Vetter says that all these muscles are innervated by spinal 
nerves. 
The coracobranchiales of the adult Acipenser are thus said 
to be so completely fused with the coracoarcuales anterior and 
posterior that they appear as simple tendons of those muscles, 
and Edgeworth says (loc. cit., p. 235) that these tendons 
are developed from downgrowths of the lower ends of the 
first, second, third, and fifth branchial myotomes, while the 
coracohyoideus, which is Vetter’s coracoarcualis anterior 
together with the tendon inserted on the hypohyal, is said (loc . 
cit., p. 268) to be of spinal origin. No downgrowth, giving 
rise to a coracobranchialis, takes place in the fourth arch, 
this arch thus forming, for some inexplicable reason, a marked 
exception to the other arches. 
This interpretation of these several muscles of Acipenser, 
based by Vetter on anatomical and by Edgeworth on embryo- 
logical investigations and considerations, may perhaps be the 
correct one, but I strongly doubt it. Comparing the condi- 
tions in this fish with those in Heptanchus, Scyllium, and, 
Mustelus, as I have described them, it seems much more 
probable that the so-called coracobranchiales of the first 
three branchial arches of Acipenser are simply the homo- 
logues of the proximal fibres of the ventral ends of the con- 
