610 EDWARD PHELPS ALLIS, JR. 
epal element of the arch, and also because of the difference in 
the manner of innervation of the adductor hyomandibularis and 
the interarcuales dorsales II of the branchial arches, from the 
hyal member of which latter muscles the inferior igament of 
the Selachii is apparently derived. 
The hyomandibula of the Teleostei is thus seen, if I am correct 
in my conclusions, to have assimilated interarcual and extra- 
branchial cartilages related to the hyal arch and by that means to 
have acquired articulation with the auditory capsule dorsal to the 
vena jugularis and in protective relation to it. If these interar- 
cual and extrabranchial components of the teleostean hyoman- 
dibula were to fuse with the auditory capsule at the places where 
they actually articulate with it, as the interarcual cartilage actu- 
ally does in Ceratodus, and, if the primitive dorsal end of the 
pharyngeal component were also to fuse with that capsule ven- 
tral to the vein, as it also actually does in Ceratodus, conditions 
would arise in the hyal arch of the Teleostei which would seem 
to be exactly similar to those actually found in the mandibular 
arch of Ceratodus (Allis 14 ¢); the anterior articular head of the 
teleostean hyomandibula being the serial homologue of the pro- 
cessus ascendens palatoquadrati of Ceratodus, the posterior ar- 
ticular head being the serial homologue of the processus oticus 
palatoquadrati, and the pharyngeal element of the hyomandib- 
ula the serial homologue of the processus basalis palatoquad- 
rati. The correspondence is in every way too exact to leave any 
doubt of this, in so far, at least, as the last two processes are con- 
cerned. The processus ascendens might equally well be, so far 
as its relations to the nerves and blood vessels are concerned, 
the extrabranchial of the premandibular arch, and, furthermore, 
there seems here no reason, as in the hyal arch, for an interarcual 
cartilage to have acquired contact with the cranial wall dorsal 
to the vena jugularis. But however this may be, the derivation 
of these three processes of the palatoquadrate from elements 
that are, in the branchial arches of the adults of living fishes, 
found either as wholly independent cartilages or fused one with 
the other or with the epal element of their arches, explains how 
they can be, in certain fishes (Ceratodus), fused with both the 
