MAXILLARY AND VOMER BONES OF POLYPTERUS 363 
laterally, its ventral end being free and its dorsal end attached 
to the side of the head by two sheets of integumental tissue, one 
of which extends to the lateral edge of the ectopterygoid and the 
other to the dorsal edge of the mandible. These two sheets of 
tissue enclose between them a dorsolateral diverticulum of the 
buccal cavity similar to that in Amia, and it corresponds, in 
position, to what Greil (713) calls, in Ceratodus, the preman- 
dibular furrow (Praemandibularfalte). This furrow is a direct 
posterior continuation of the maxillary preangular crease, and, 
diminishing in depth posteriorly, vanishes near the quadrato- 
mandibular articulation. Posterior to the angle of the gape, 
the ascending process of the splenial rises in the integumental 
sheet that connects the dorsal end of the labial cartilage with the 
dorsal edge of the mandible, and the dorsal end of the labial now 
becomes attached to the dorsal end of this process. This 
process of the splenial is called by Traquair (’70) the opercular 
process, but it is the homologue of that process of reptiles, 
formed by the so-called complementary, and not of the opercular 
process of Amia, which is a process of Meckel’s cartilage and 
wholly wanting in Polypterus. 
The labial cartilage is, as described in my earlier work, some- 
what triangular in shape, with a long straight dorsoposterior 
edge, and anterior and anteroventral edges that are somewhat 
rounded and separated by a rounded angle. The ventral corner 
of the cartilage is also rounded, but a pad of tough ligamentous 
tissue lies against the posterior surface of this rounded angle 
and gives to the entire structure a right-angled postero- 
ventral corner, the posterior edge of this angle lying in the line 
of the straight posterior edge of the labial cartilage, while the 
ventral edge forms a short straight ventral edge to that cartilage. 
The anterior end of this so-formed short ventral edge of the 
labial cartilage lies directly posterior to the secondary angle 
of the gape, its hind end forming the ventral end of the posterior 
edge of the labial fold. There is no furrow running from the 
angie of the gape across the labial fold and corresponding to the 
submaxillary furrow of Acanthias. When the mouth is widely 
opened (fig. 4), the labial cartilage lies in a nearly horizontal 
THE AMERICAN JOURNAL OF ANATOMY, VOL. 25, No. 4 
