MAXILLARY AND VOMER BONES OF POLYPTERUS 355 
alveololabial suleus of Acanthias. This sulcus .begins, pos- 
teriorly, somewhat anterior to the transverse plane of the angle 
of the gape, and is there a’slight furrow along the lateral edge 
of the ectopterygoid, but farther forward it becomes a small but 
well-developed groove. Still farther forward, in the region of 
the anterior end of the dermopalatine, the internal edge of this 
groove begins to flatten out, the external edge at the same time 
increasing in height and becoming the slightly developed maxil- 
lary breathing-valve. That valve is thus formed by the an- 
terior portion of the primary lip of the fish, the posterior portion 
of that lip being represented in the lateral edge of the slightly 
developed primary alveololabial sulcus. In a 45-mm. specimen, 
the line of origin of this lip lies wholly internal to that of the 
labial fold. In one of two adult specimens examined, its external 
surface had partly coalesced with the internal surface of the 
fold in the region of the anterior end of the maxillary, this 
undoubtedly being an initial step in that attachment of the base 
of the breathing-valve to the internal surface of either that 
bone or the premaxillary that is probably found in most, but 
certainly not in all, of the Teleostei, for in small specimens of 
Ameiurus this fusion does not take place, the primary lip 
(breathing-valve) having strictly the course and position that it 
has in Amia, and everywhere projecting as a definite lip. 
Lateral to the posterior portion of the primary upper lip, 
_there is a maxillary preangular crease, which extends upward 
lateral to the bottom of the supralabial furrow, these two furrows 
enclosing between them a thin sheet of integumental tissue which 
connects the dorsal end of the labial fold with the side of the 
head slightly dorsal to the lateral edge of the roof of the mouth. 
This crease is directly continuous, posterior to the angle of the 
gape, with a dorsally directed diverticulum of the buccal cavity 
which lies along the lateral edge of the palatoquadrate, and, con- 
tinuing posteriorly, vanishes in the region of the angle of the 
primary gape. This diverticulum is thus the homologue of the 
deep furrow that lies in Acanthias, along the lateral edge of 
the posterior portion of the palatoquadrate of that fish, and in 
both fishes it lies posterior to the secondary angle of the gape. 
