360 EDWARD PHELPS ALLIS, JR. 
tegumental tissue which connects the labial fold with the lateral 
surface of the head immediately dorsal to the bases of the maxil- 
lary teeth. Proceeding posteriorly in the sections, these two 
furrows deepen, the bottom of the maxillary labial-flap furrow 
passing downward lateral to that of the secondary alveololabial 
sulcus and diverging gradually from it. The narrow band of 
integumental tissue that connects the anterior end of the labial 
fold with the side of the head thus becomes considerably widened, 
and, at the same time gradually thickening, becomes the deeper 
and larger part of the maxillary portion of the entire labial fold. 
Farther posteriorly, where the anterior end of the supralabial 
furrow is first cut in the sections, the bottom of that furrow is 
directed toward the bottom of the secondary alveololabial sulcus, 
the bottoms of these two furrows there enclosing between them 
a thin and narrow band of integumental tissue which connects 
the labial fold with the side of the head. Proceeding posteriorly 
from there, the supralabial furrow deepens, its bottom passing 
downward lateral to that of the alveololabial sulcus, and the 
anterior end of another furrow is soon cut in the sections. This 
latter furrow lies lateral to the secondary alevololabial sulcus 
and lateral also to the bottom of the supralabial furrow, and as 
its course and position indicate that it is quite certainly the 
homologue of the maxillary preangular crease of Acanthias, it 
may be so designated. The supralabial furrow now gradually 
becomes arched in transverse section, running at first upward 
and then downward beneath the canal-bearing component of the 
maxillary bone, and when the region of the lateral process of the 
ectopterygoid is reached, the dorsal portion of the labial fold is 
wholly concealed beneath the overhanging, canal-bearing com- 
ponent of the maxillary. The anterior portion of the labial car- 
tilage is here cut in the sections, and the sheet of integumental 
tissues that connects the dorsal end of the labial fold with the 
side of the head is, when the mouth is closed, markedly U-shaped 
in transverse section. When the mouth is opened and the labial 
fold extended, this ‘U’ is pulled out into a flat sheet, but its 
proximal and distal (labial) edges are still marked, respectively, 
by the bottoms of the secondary alveololabial sulcus and the 
maxillary preangular crease. 
