MAXILLARY AND VOMER BONES OF POLYPTERUS 359 
that they have a greater anterior extension, which is doubtless 
due simply to the greater extension of the secondary lip. 
Slightly posterior to the nasal tube, the labial-flap furrow 
crosses the anterior section of the main infraorbital laterosensory 
canal, passing across the primary tube that issues from that 
eanal between the lachrymal bone and the antorbital process of 
the premaxillary. If the furrow were to be here deepened, it 
would evidently interfere with the development of the latero- 
sensory canal, and this is apparently what has taken place in 
many of the Teleostei, for a furrow is there found that is either 
the homologue of this labial-flap furrow or is a closely adjacent, 
but independent furrow, and it extends across the dorsal surface 
of the anterior end of the snout to fall into its fellow of the 
opposite side. In all such fishes, so far as I know, the antorbital 
section of the infraorbital canal is short, or even wholly want- 
ing, and associated with this absence of the canal there is no 
independent antorbital bone. Furthermore, it is, so far as my 
material permits me to judge, only in these fishes that the pre- 
maxillary is prolonged more or less posteriorly into the labial 
fold, and that the upper jaw becomes more or less protrusive. 
The supralabial furrow of Polypterus begins near the anterior 
edge of the eyeball, along the ventral edge of the lachrymal 
bone, as a slight furrow which lies internal to the dorsal edge of 
the maxillary labial flap. Proceeding posteriorly from there, 
this furrow deepens and soon becomes a deep cleft which arches 
upward beneath the laterosensory component of the maxillary 
bone and then downward to a line that lies, in its anterior por- 
tion, lateral to the bases of the maxillary teeth, but, in its 
posterior portion, along the lateral edge of the ectopterygoid. 
On the roof of the mouth, internal to the labial fold and im- 
mediately external to, and concentric with, the premaxillo- 
maxillary dental arcade, there is a furrow which, because of its 
relations to that arcade, may be called the secondary superior 
alveololabial sulcus. The bottom of this sulcus is, in the region 
of the anterior end of the maxillary labial-flap furrow, directed 
toward the bottom of that furrow, the bottoms of the two fur- 
rows being separated from each other by a narrow band of in- 
