LIPS AND NASAL APERTURES IN FISHES 181 
men it is simply a somewhat posteriorly directed process, or 
prolongation, of the so-called subnasal cartilage, the outer end 
of this process reaching and being strongly attached by liga- 
mentous tissues to the so-called postnasal cartilage of Fir- 
bringer’s descriptions, but not being continuous with it. The 
lateral prolongation of the subnasal cartilage beyond this cross- 
bar, shown in Fiirbringer’s figure, is, in my specimen, simply a 
band of tough ligamentous tissue which runs forward along the 
lateral edge of the anterior nasal aperture and is lost in the 
tough tissues of the upper lip. The latero-sensory canals of this 
fish all lie aboral (dorso-posterior) to both the nasal apertures, 
and aboral also to the upper lip, this being the relations that 
they have, in the Holocephali, to the nasal apertures and the 
supramaxillary fold of those fishes. 
Comparing the conditions in this fish, as thus described, with 
those in the Plagiostomi, it seems certain that the anterior and 
posterior nasal apertures of these fishes are respectively homolo- 
gous. The so-called subnasal cartilage of Ceratodus must 
then be a remnant of the alar cartilage of the Plagiostomi, for 
that this cartilage of Ceratodus, spanning as it does the primitive 
single nasal opening, can be a persisting remnant of any part of 
the walls of the nasal capsule is evidently impossible, those walls 
encircling the primitive nasal opening and not spanning it. 
This cartilage is said to be found, in Lepidosiren, fused at its 
lateral end with the edge of the nasal capsule and there appear- 
ing as a process of that capsule, and this would be in accord with 
Gegenbaur’s derivation of the alar cartilage from the outer edge 
of the nasal capsule, but in Ceratodus it is an independent 
cartilage, and this would seem to be its primitive condition. 
The posterior process of this cartilage, as I find it, the cross-bar 
of Furbrimger’s descriptions, must then also be a part of this . 
alar cartilage, and the ligament which lies along the lateral edge 
of the anterior nasal aperture, a further but unchondrified por- 
tion of it. The postnasal cartilage is, for reasons given im- 
mediately below, quite certainly not a part of this alar cartilage, 
and would seem to be the homologue of the cartilage ‘f’ of 
Hubrecht’s (77) descriptions of Chimaera and Callorhynchus, 
