76 
ZOOLOGY: E. P. ALUS 
nasal apertures of Ceratodus are accordingly enclosed in the buccal 
cavity so enlarged, but as I can not trace the secondary upper lip in 
my specimen of this fish I can not tell whether they both lie in the ter- 
tiary addition to that cavity or one of them in that part of the cavity 
and the other in the secondary addition to it. No tertiary lower lip 
is formed, the tertiary upper lip simply overlapping the secondary lower 
lip. The anterior dental plates of this fish lie immediately internal to 
a lip that would seem to be a primary one, but as I cannot trace the 
secondary lips I cannot definitely affirm this. In Chimaera the corre- 
sponding plates lie internal to the primary lips, and hence belong to the 
palatoquadrate arcade. 
In the Amniota the definitive upper lip is a secondary one, and it 
passes between the two definitive nasal apertures. Maxillary and pre- 
maxillary bones are developed in relation to it, and it is certain, from 
conditions found in certain of the Sauropsida, that the internal nasal 
aperture lay primarily between this arcade and the vomero-palato- 
quadrate arcade. The palatine bone of certain of these latter vertebrates, 
however, develops laterally and anteriorly, either approaching, coming 
into contact with, or even fusing with the maxillary or premaxillary 
bones, and in Chelone a ventral process of the bone turns antero-mesially 
and fuses with a ventral plate of the vomer anterior to the definite pos- 
terior nasal aperture. The posterior nasal passage of this animal thus 
lies between dorsal and ventral plates of both the vomer and the pala- 
tine, and the definitive choana, which is a secondary one, lies posterior 
to the ventral plates, the primary choana lying, as it normally should, 
anterior to the dorsal plates and hence to the bodies of the palatine and 
vomer. An accentuation of these conditions would withdraw the pala- 
tine bone entirely from its own arcade and leave it definitely anterior 
to the choana, as it is in the human skull, but it there nevertheless still 
lies posterior to the primitive choana. 
In embryos of all of the gnathostome vertebrates above considered, 
the primary lips are represented in the edges of the primary stomo- 
daeum., and hence not only in the deeper portions of the so-called maxil- 
lary and mandibular processes but also in the tissues that lie between 
the anterior (symphysial) ends of those processes. In embryos of the 
Teleostomi and Plagiostomi, excepting Heterodontus and those other 
Plagiostomi in which similar conditions may exist, the secondary lips 
are represented in the superficial portions of these same processes, and the 
maxillary processes, like the secondary upper lips of the adult, in 
growing forward pass oral to the nasal apertures, and they alone, or they 
together with an intervening portion of the primary upper lip, form the 
