LIPS AND NASAL APERTURES IN FISHES 163 
mesial border of the alar ring, supports the external (ventral) 
wall of this latter passage and corresponds to the flat recurved 
end of the alar cartilage shown in Daniel’s figure of this fish. 
The point where the alar cartilage is fused with the outer edge 
of the nasal capsule lies between this little process and the 
process 6. 
The ala nasalis of all of the Plagiostomi was considered by 
Gegenbaur to be a part of the chondrocranium, and not, as J. 
Miiller (34) had previously concluded, an originally independent 
skeletal element which had secondarily fused with the outer 
edge of the nasal capsule. Huxley (76) and Parker (’76) must 
both have accepted Miiller’s view, for they both (Huxley in 
Heterodontus and Parker in Scyllitum and Raia) describe this 
cartilage as a labial. Gaupp (06) however considers Gegen- 
baur’s conclusion to be confirmed by conditions in an 8 cm. 
embryo of Mustelus, the Nasenfliigelknorpel being said to there 
be ‘‘in kontinuierlicher Verbindung mit der Nasenknorpel.”’ In 
a 122 mm. embryo of Mustelus vulgaris I find the cartilage every- 
where definitely and distinctly separate from the nasal capsule, 
but the two cartilages are connected by a line of tissue which 
is a continuation of two thin layers of tissue which are closely 
applied, one to the external and the other to the internal surface 
of both these cartilages, and which apparently represent thick 
perichondrial membranes similar to the one that I have described 
on the external surface of these cartilages in the adult Mustelus. 
In a 55 mm. embryo of this same fish the ala nasalis is also 
everywhere definitely separate from the capsule, but at one 
point the two cartilages closely approach each other and are 
connected by dense tissue continuous with that which lines both 
surfaces of these cartilages. This tissue does not however here 
undergo chondrification, for it persists as fibrous or connective tis- 
sue in the olderembryo. The alar cartilage is thus quite certainly 
not cut off from the edge of the nasal capsule in the ontogenetic 
development of this fish, but it is developed in a layer of em- 
bryonic tissue which is continuous with that in which the cap- 
sule and adjacent portions of the chondrocranium are developed. 
There seems however no more reason, simply because of this, 
