194 EDWARD PHELPS ALLIS, JR. 
Holocephali, to the tubules of ampullary sacs which lie on the 
dorsal surface of the snout, is represented, in the Mammalia, by 
a groove which later becomes connected with a glandular 
structure also lying in this region. 
The position of the secondary upper lip—in certain instances 
oral to the two nasal apertures and in others passing between 
them—depends upon the position, at the time the fold of this 
lip pushes forward, of the nasal apertures relative to the upper 
edge of the mouth, and also upon the height of the fold and the 
length of the gape of the mouth. Where the gape is short and 
the fold of the lip is high, as in Heterodontus, the fold naturally 
passes between the two apertures. The extent of the cranial 
flexure at the time of the formation of the fold may also have 
some influence on its relations to the nasal apertures. 
The importance and wide distribution of the labial and supra- 
maxillary folds would seem to indicate that the furrows related 
to those folds can not be simple adventitious creases in the 
external dermis, and the evident inference is that they may 
represent persisting remnants of a premandibular cleft or clefts. 
This, if so, would not affect any of the conclusions I have arrived 
at, for the related arch or arches would still necessarily le 
morphologically posterior to the oral plate of embryos. The 
mouth could not, however, in that case, be developed from the 
mandibular branchial clefts fused with each other in the mid- 
ventral line, for the edge of mouth lies anterior to all the labial 
folds and furrows. The mouth would then, of necessity, be a 
terminal opening formed by the breaking through of the 
anterior wall of the gut, that wall being represented in the oral 
plate of embryos. 
In the Cyclostomata the upper lip lies between the hypoph- 
ysis and the oral plate, and it is highly probable that it repre- 
sents the primary lip of all vertebrates. If this be so, the lips 
in these fishes are, as compared with those in other vertebrates, 
primitive and not degenerate structures. His calls this lip the 
‘Schnauzenfalte,’ but it is certainly not the ‘Schnauzenfalte’ of 
his descriptions of the Mammalia. The supramaxillary fold of 
the Holocephali and Dipneusti is perhaps represented in the 
