186 EDWARD PHELPS ALLIS, JR. 
10), there are said to be no ‘lips’ (Géeppert, ’06, p. 79), and 
hence, of course, no cheek. 
In embryos of all of the gnathostome fishes above considered, 
the primary lips of either side of the head are at first represented 
in the corresponding half of the edge of the primary stomodaeum. 
When the so-called maxillary and mandibular processes of either 
side later begin to develop, they overlie and include the absym- 
physial portions of this edge of the stomodaeum, leaving the 
symphysial portions of that edge exposed between their anterior 
(symphysial) ends and the corresponding ends of the processes 
of the opposite side, as shown in figures of embryos of all of these 
fishes. The mandibular processes of opposite sides always, in 
these figures, ultimately meet and coalesce at the symphysis, 
but the conditions in the adult show that this can not take place 
in all of the Plagiostomi. The maxillary processes of opposite 
sides, on the contrary, do not always meet and coalesce at the 
symphysis in these embryos, as is well shown in Géeppert’s 
(06) figures of embryos of Torpedo and Mustelus and Keibel’s 
(06) figures of embryos of Acanthias, a portion of the edge of 
the primary stomodaeum, which represents a corresponding part 
of the primary upper lip, always remaining exposed between 
them and forming the median portion of the definitive upper lip. 
Keibel (06, p. 157) calls attention to the fact that, in embryos 
of Acanthias, the middle portion of the upper lip is not formed - 
by the maxillary processes, and, although he could not determine 
from what it was formed, he questions its origin from the 
fronto-nasal process. It is, in fact, not formed by that process, 
properly so-called, for the oral edge of the process is formed by 
the crest of the fold of the secondary upper lip, and the fronto- 
nasal process, properly so-called, only occurs where the secondary 
upper lip crosses some part of the nasal groove and has been cut 
in two by its encounter with it. This takes place in Hetero- 
dontus, and probably also in certain others of the Plagiostomi 
in which there is a naso-buccal groove, but it does not take place 
in any of the Plagiostomi in which there is no naso-bucéal groove, 
nor in any of the Teleostomi, the secondary upper lip there 
always passing between the upper edge of the mouth and the 
