LIPS AND NASAL APERTURES IN FISHES 193 
(06, p. 157) that, in all vertebrates, from the Selachii upward, 
the upper edge of the mouth les anterior to the hypophysis, is 
accordingly not wholly correct. 
The primitive invagination of the mouth, or primary stomo- 
daeum, certainly lies posterior to the primary lips, whatever 
the relations of those lips to the hypophysis may have been, and 
it is represented only in the deeper portion of the depression 
enclosed between the so-called mandibular, maxillary and fronto- 
nasal processes of embryos, the remainder of that depression 
representing the space between the primary and secondary lips. 
The stomodaeum of current descriptions of vertebrate embryos 
is accordingly something more than the primary stomodaeum, 
being, in all the gnathostome vertebrates excepting the Dipneusti, 
largely a portion of the external surface of the head which is in 
process of being secondarily enclosed between the primary and 
secondary lips, and, in the Dipneusti, being largely a space in 
process of being enclosed between the primary and tertiary 
lips. 
The Schnauzenfalte of His’s (’92 b) descriptions of vertebrate 
embryos is quite certainly, in certain instances, either the 
primary or secondary upper lip. In embryos of the Mammalia 
it has strikingly the position of the median portion of the supra- 
maxillary fold of the Holocephali and Dipneusti, but it seems 
probable that it is not that fold but a special formation peculiar 
to the Mammalia, the supramaxillary fold being limited to the 
extent that it has in the Teleostomi, and being represented in 
that portion of the maxillary process of embryos of the Mammalia 
which bounds the lacrimal groove laterally and which is well 
shown in Keibel’s (’93) figures of embryos of the pig. The fact 
that the lacrimal canal of the adult mammal lies between the 
lacrimal bone and the nasal spine of the maxillary bone, and the 
probability that the lacrimal and antorbital bones of Amia repre- 
sent, respectively, the lacrimal bone and the nasal spine of the 
Mammalia, is in favor of this supposition, for it is at just this 
place that the anterior end of the supramaxillary furrow turns 
upward and ends in Amia. If this be so, it seems worthy of 
note that a furrow beneath a fold definitely related, in the 
JOURNAL OF MORPHOLOGY, VOL. 32, No. J 
