HYOMANDIBULA OF THE GNATHOSTOME FISHES 605 
chial of the arch, and its relatively late and sudden development 
are also in accord with.its being that element. That it can be 
the homologue of the symplectic of the Teleostomi, to be later 
considered, seems quite improbable. The only remaining carti- 
lage, Eh, is then the epihyal, and it has all the relations to the 
adjacent structures of such anelement. All the cartilages in this 
arch of Ceratodus are thus those normally found in a visceral 
arch and they could all have been readily derived from a con- 
dition resembling but preceding that actually found in the Tor- 
pedinidae. 
The Teleostomi can now be considered; and here, as with the 
Elasmobranchii and Dipneusti, the descriptions of the develop- 
ment of the hyal cartilages are conflicting. For the purposes of 
this paper it will suffice to refer only to Edgeworth’s somewhat 
recent work. 
Edgeworth says (11, p. 207) that in 8 mm. embryos of Acipen- 
. ser the hyal bar is still in a procartilaginous and unsegmented 
condition and does not extend up to the auditory capsule. The 
nervus hyomandibularis facialis is said to pass “‘over the upper 
end of the bar and then downwards outside it,’ which would 
seem to be simply the relation that the branchial nerves of the 
adult have to the cartilaginous bars of the related branchial 
arches. In 8} mm. embryos of this fish the hyal bar is said to 
extend upward in front of ‘and outside’ the nervus hyomandib- 
ularis facialis, and the definitive hyomandibula is said to be 
formed from this upgrowth together with the upper portion of 
the primitive bar, when that bar later segments. The hyoman- 
dibula is thus here said to develop exactly as it is claimed by 
Edgeworth (1. ¢., p. 206) to develop in Scyllium, differing only in 
that the upgrowth of the hyal bar toward the auditory capsule 
is said to pass anterior to the nervus facialis in Acipenser while 
no mention is made of the relations of the upgrowth to the nerve 
in Scyllium. No mention is made by Edgeworth either of a 
symplectic or an interarcual cartilage. 
In Polypterus the hyomandibula is said by Edgeworth to de- 
velop exactly as in Acipenser, no account apparently being taken 
of the important fact that the relations of the hyomandibula to the + 
