LIPS AND NASAL APERTURES IN FISHES 185 
The primary upper lip lies immediately external to the teeth 
developed in relation to the palatoquadrate. The secondary 
upper lip lies immediately external to the maxillary and pre- 
maxillary teeth. The tertiary upper lip has no teeth developed in 
relation to it, but in the Teleostei and Holostei the corresponding 
supramaxillary fold encloses the oral edges of the lacrimal and 
anterior suborbital bones. 
In the Amniota the functional lips are the secondary ones, 
and the secondary upper lip passes, in all these vertebrates, 
between the two nasal apertures. Maxillary and premaxillary 
teeth or bones may be developed, as in the Teleostei, Holostei, 
and Crossopterygil, in relation to this secondary upper lip. In 
most of the Sauropsida both of these latter bones are actually 
developed in relation to this lip, and there are, accordingly,.in 
the upper jaw of these vertebrates, as in the Teleostei, Holostei, . 
and Crossopterygii, two arcades, with or without teeth, an 
inner and primary arcade formed by the bones developed in 
relation to the palatoquadrate and an outer and secondary 
arcade formed by the maxillary and premaxillary bones; and 
the posterior nasal apertures lie between these two arcades. In 
certain of the Sauropsida a secondary palate is formed by ventral 
plates of the vomer and palatine, and the definitive choana lies 
posterior to the plate so formed, but the primary choana never- 
theless still les anterior to the dorsal and primary portions of 
those bones. In the Mammalia this same relation of the 
posterior nasal apertures to the two arcades must also persist, 
but I am not familiar enough with these vertebrates to discuss 
the conditions there. Comparison with fishes would however 
suggest that the presence of a cheek in the Mammalia ditremata 
is due to a marked reduction of the maxillary bone, as in 
Polypterus (Allis, ’00), and its fusion with the pterygoid, this 
then accounting for the absence in these animals of the latter 
bone, as claimed by Gaupp (710). And it may be further 
mentioned, as a curious coincidence, that a dimple is found in 
the cheek of man in approximately the position of the post- 
labial furrow of fishes. In the Mammalia monotremata, where 
the pterygoid persists in normal reptilian position (Gaupp, 
