MAXILLARY AND VOMER BONES OF POLYPTERUS 371 
ventrolateral, edge of the palatoquadrate cartilage. The ptery- 
goid bone is also of membrane origin, and I find, in my speci- 
mens, no indications of the so-called ectosteal scales described 
by Bridge and said by him to probably represent mesopterygoid 
elements. 
The maxillary splint lies in the upper lip of the fish, and the 
posterior portion of this lip overlaps externally the dorsal edge 
of the mandible, this overlapping portion of the lip enclosing 
the ventral corner of the orbitar process of the palatoquadrate, 
but no portion of the maxillary splint. A slight labial sulcus lies 
along the external surface of the ventral edge of the anterior 
portion of the maxillary splint and separates the teeth on that 
splint from the definitive and quite small upper lip. There is 
no slightest indication of a supralabial furrow, but that furrow 
and the overlying supralabial fold are apparently well de- 
veloped in embryos of Acipenser, as shown in my recent work 
(Allis, ’18), the fold and furrow there being called the supra- 
maxillary ones. In the mandible there is a short furrow 
which extends upward a short distance immediately posterior to 
the angle of the secondary gape, and it is apparently the homo- 
logue of the sublabial furrow of Polypterus and the Selachii, 
and in apparent correlation to this there is no coronoid process 
to Meckel’s cartilage. 
The conditions in this fish are thus similar to those in 114-mm. 
embryos of Amia, excepting in that the furrow in the mandible 
is probably a sublabial one instead of a mandibular labial-flap 
furrow. ‘The posterior portion of the upper lip of Polyodon is 
then certainly a secondary lip, and the slightly differentiated 
labial fold is probably, as in Polypterus, a maxillomandibular 
one. The orbitar process of the palatoquadrate, which lies in 
this fold, must then be a labial cartilage, as Gegenbaur (’98 
p. 342) concluded, but there seems nothing to indicate that it 
is a posterior upper labial alone, as Gegenbaur concluded, rather 
than a cartilage formed by the fusion of both upper labials, for 
the labial fold certainly encloses the primordia of both upper 
labials. This upper labial, or labials, of Polyodon having fused 
with the palatoquadrate, supralabial, and submaxillary furrows 
could naturally not be developed. 
