No. 3.] CHEEK AND SNOUT OF AMIA CALVA. 453 
lary lies mesial to the nasal capsule, and may extend backward 
beyond the anterior end of the frontal, always lying, in such 
cases, superficial to that bone. In certain of Parker’s figures 
it is shown internal to the nasal bone (Pl. XIX, Fig. 4); in 
others it seems to lie external to that bone (Pl. XV, Fig. 5) ; and 
in still others (Pl. XX, Figs. 1 and 3) it seems to be completely 
or incompletely separated into two parts, the posterior of which 
lies external to the frontal. It always lies mesial to the nasal 
bone. 
Is, then, the so-called ascending process of the premaxillary 
of Amia, which lies internal to the ethmoid and nasal bones 
and ventral to the nasal sac of the fish, the homologue of the 
‘similarly named process of teleosts and urodeles which always 
lies external to the ethmoid, and either anterior to, or mesial to, 
the nasal bones and nasal capsules? It seems to me most 
improbable, and I look for the homologue of the ascending 
process of teleosts and urodeles either in some small part of 
the posterior process of Amia fused with the ethmoid bone of 
that fish, or in the latter bone alone. This latter possibility 
for a part of the ascending process of Szven /acertina seems to 
have already been suggested by Wiedersheim (quoted No. 16, 
Bd. I, p. 109). The small median bone considered by Sage- 
mehl, in the Cyprinidae, as the ossified rostrale is then simply 
the ethmoid bone of Amia greatly reduced. The large, lateral 
ascending process of Polypterus I consider, as already stated, 
as the antorbital bone of Amia fused with the premaxillary. 
What, then, is the posterior process of the premaxillary bone 
of Amia? Its general shape, its relation to the nasal sac, and 
its perforation by the olfactory nerve seem to me to indicate, 
almost conclusively, that it is a bone developed in relation to a 
lateral sense organ that has given origin to the sensory epithe- 
lium of the nose, just as the different sections of the several 
canal bones are developed in relation to the sense organs they 
are destined to protect or enclose. The nasal sense-organ bone 
has simply retained its larval form, and fused with the tooth- 
bearing premaxillary plate which lies immediately in front of 
it. The piercing of the premaxillary bone by the ramus pala- 
tinus anterior facialis, simply to reénter the bone again from 
