LIPS AND NASAL APERTURES IN FISHES 161 
Ceratodus are concerned, but incorrect as to the formation of 
this aperture, in the latter fish, by the bridging of a naso-buccal 
groove, as Greil (713) has shown and as will be fully discussed 
later. Furthermore, it may here be stated that the assumption, 
frequently made, that the bridging of a naso-buccal groove, as 
that groove is currently described in certain of the adult Plagi- 
ostomi and in embryos of these and other vertebrates, could 
produce two nasal apertures the homologues of those actually 
found in the adult gnathostome fish is an error. The naso- 
buccal groove, as described both in the adult and in embryos, 
is said to extend either from the oral edge of the oral (posterior) 
nasal aperture, or from that edge of the nasal pit, to the upper 
edge of the mouth, the primitive oral (posterior) nasal aperture 
accordingly lying aboral to the aboral end of the groove, and 
between that end of the groove and the incompletely formed 
nasal bridge. If then this nasal bridge were to be completely 
formed, and the naso-buccal groove were to be bridged by the 
fusion of its opposite edges, the fusion of this bridge with the 
nasal bridge would give rise to a secondary posterior nasal 
aperture which would not be the homologue of the aperture 
actually found in fishes, while the formation of a naso-buccal 
bridge alone, without the formation of a proper nasal bridge, 
would give rise to an external nasal aperture which would corre- 
spond to the undivided primitive single opening of the nasal 
pit, and to an internal aperture which would have no homologue 
in fishes. 
The ala nasalis of Heterodontus (Cestracion) philippi has 
been carefully described and figured by Gegenbaur (’72), and it 
is said by him to be a complete ring, surrounding both nasal 
apertures, and quite extensively fused, at two points, with the 
cartilage of the nasal capsule. Huxley (’76) also described and 
figured this cartilage in this fish, but as a partial and not a 
complete ring, and he makes no mention of its being anywhere 
fused with the edge of the nasal capsule; both of which details 
are in accord with his conclusion that this cartilage is an upper 
labial cartilage. Daniel (15) has also described and figured this 
cartilage in Heterodontus francisci, and he also does not find it 
JOURNAL OF MORPHOLOGY, VOL. 32, No. 1 
