110 
EDWARD PHELPS ALLIS. 
tions of the Batoidei, the nasal-flap cartilage of the present 
descriptions, can not accordingly be the homologue of either 
of the labial cartilages of that author’s descriptions of the 
Selachii, and it is apparently a fibro-cartilage developed 
wholly in supporting relation to the nasal flap. Sections of 
it show the interior of the cartilage a mass of fibrous strings 
running gradually, toward the exterior on either side, into 
hyaline cartilage. 
The nasal-flap cartilage of Raia thus not being the liomo- 
logue of either of the labials of the Selachii, the single upper 
labial of the former fish might represent either one of the 
labials of the latter fishes. I am, however, strongly inclined 
to believe that it represents both the labials of the latter 
fishes, here secondarily connected by a narrow neck of 
cartilage ; the mesial and lateral portions of the labial of 
Raia representing', respectively, the anterior and posterior 
labials of the Selachii. The general shape and disposition of 
the cartilage favours this view, and this composition of the 
labial would offer a possible explanation of the peculiar course 
of the nasal latero-sensory canal. The labials, in the Selachii,. 
lie either oral or internal to the nasal latero-sensory canal, as 
just above explained. In Raia the labial lies in large part 
aboral to the canal, and, in acquiring this position, the two 
parts of which I consider the labial to be composed have 
necessarily pushed against and carried with themselves those 
branches of the nervus buccalis lateralis that supply the 
organs of the related portion of the caual. This push on the 
nerves would naturally tend to displace the caual, but 
the mesial section of the canal was held in place by the 
attachment of the nasal-flap cartilage to the lateral end 
of the anterior labial. The lateral portion of the canal was 
not so held in place, and would in consequence be carried 
aborally by the pull of the nerves, and these nerves, becoming 
more or less enveloped in the pushing edge of the labial,, 
would be found perforating the cartilage in the adult. The 
sharp bend actually found in the canal would thus be 
accounted for. The relations of the nerves to the mesial 
