LIPS AND NASAL APERTURES IN FISHES 165 
other antero-mesial, instead of, as in all the Plagiostomi, one 
antero-lateral and the other postero-mesial, and it is the antero- 
mesial aperture of Chimaera which is currently considered to be, 
and probably is, the incurrent aperture. The postero-lateral 
aperture lies not far from the lateral edge of the palatoquadrate, 
nearer to it than the antero-mesial aperture, and a short naso- 
buccal groove leads from it to the lateral edge of the palatoquadrate 
immediately anterior to the inner end of the line of the angle 
of the gape. The line joining the two nasal apertures lies in a 
nearly horizontal position, extending from the antero-mesial 
aperture, laterally and posteriorly and inclining slightly toward 
the lateral edge of the palatoquadrate. The Schneiderian mem- 
brane lies at the bottom of a relatively deep nasal capsule, as an 
elliptical rosette, the long axis of which lies in a nearly horizontal 
position, transverse to the axis of the body, and at a marked 
angle with the line of the nasal apertures, thus having practically 
the position that it has in most of the Plagiostomi. 
The middle portion of the upper lip is formed by a thick pad 
of tough dermal and subdermal tissues which has the width of 
the vomerine teeth, this portion forming the premaxillary upper 
lip of Huxley’s (76) descriptions, and bounding antero-mesially 
the naso-buccal groove. Along the oral edge of this lip there is 
usually, but not always, a shallow but well defined suleus which 
separates the lip into thin oral and thick aboral portions. The 
oral portion is certainly a primary upper lip. The aboral por- 
tion has the position of a secondary upper lip, but as it is quite 
certain that it is formed, not by the fold of the secondary lip, 
but by the oral edge of the nasal flap which has been turned 
back upon the dorsal surface of the snout and has there coalesced 
with the external dermis, it will be best to call it the aboral pre- 
maxillary lip. The primary lips of opposite sides are directly 
continuous with each other in the median line. The aboral 
premaxillary lips are there separated from each other by a long - 
and deep median incisure. At the lateral edge of the pre- 
maxillary lip these two parts of the lip turn toward each other and 
coalesce, thus forming a rounded fold, the oral end of which forms 
a slightly projecting angle. Beyond this point the deeper portion 
