VISCERAL ARCHES OF THE UNATHOSTOME FISHES 387 
continuous with the posterior part of the interhyoideus, 
whilst the anterior part of the interhyoideus is inserted 
laterally into the hyoid bar.” And also (loc. cit., p. 210) 
that : “ The fore part of the interhyoideus of Acipenser forms 
the hyohyoideus inferior (Cs 5 of Vetter), the hinder part, 
i.e. the lower part of C 2 vd, forms a constrictor operculi 
(Cs 3 and Cs 4 of Vetter). In Polypterus the condition is 
similar. In Lepidosteus, Amia and Salmo, the fore part 
forms the hyohyoideus inferior ; the hinder part becomes 
attached laterally to the hyoid bar (only partially so in 
Lepidosteus) and forms the hyohyoideus superior.” 
In Amia, the superior or deeper, and the inferior or super- 
ficial portions of the geniohyoideus of my descriptions of that 
fish are respectively called by Edgeworth (loc. cit., p. 210) 
the musculus hyomaxillaris and the musculus intermandibu- 
laris posterior. The musculus hyomaxillaris, as above defined 
by Edgeworth, is said by him to be differentiated from the 
“ upper edge ” of the hyohyoideus inferior, but comparison 
with the adult shows that this so-called upper edge of that 
muscle must be the dorsal edge as seen in transverse sections 
of embryos, and hence morphologically the anterior edge of 
the muscle. In Lepidosteus and Acipenser these same fibres 
of the hyohyoideus inferior are said to form a hyomaxillaris 
ligament, and this ligament is said (loc. cit, p. 212) to be the 
ligamentum mandibulo-hyoideum of van Wijhe’s (1882a) 
descriptions of the adults of these fishes. But there is evi- 
dently some error or oversight here, for a ligamentum 
mandibulo-hyoideum is described by van Wijhe in Amia, as 
well as in Lepidosteus and Acipenser, and hence coexists in 
the former fish along with the musculus hyomaxillaris of 
Edgeworth’s descriptions. A further difficulty is that the 
musculus hyomaxillaris of Amia is said (loc. cit ., p.223) to be a 
serial homologue of the interarcuales ventrales of the branchial 
arches of that fish, notwithstanding that the former muscle 
is said to be derived from the cephalic coelom, as already 
explained, and the latter muscles to be developed from the 
ventral ends of the branchial myotomes. Edgeworth calls 
