No. 3.] CHEEK AND SNOUT -OF AMIA CALVA. 435 
cross-commissure across the top of the head. The mesial part 
of each of these bones lies directly upon the dorsal surface of a 
long, thin, anterior end, or process, of the frontal, which proc- 
ess lies directly upon the cartilage of the snout. Lateral to 
this process, bone 2 rests directly upon the cartilage of the 
dorsal surface of the snout and upon the dorsal surface of bone 
3, which bone both Bridge and Sagemehl consider as the homo- 
logue of the septomaxillary of Amia. The posterior part of 
bone 2 is covered externally by the anterior half or two-thirds 
of the nasal, but the bone itself forms no part of the roof of 
the nasal capsule, its lateral edge turning downward along the 
shelving, lateral surface of the cartilage of the snout. Its 
antero-lateral extremity articulates with the premaxillary, and 
is bound to that bone, and to the palatine bone behind it, by 
strong fibrous or ligamentous tissue. In one large specimen 
the septomaxillary lay slightly below the level of the dorsal 
surface of the rostrum, and there was a corresponding raised 
surface on the ventral surface of bone 2, which fitted into the 
depression and onto the septomaxillary. The adjoining surfaces 
of these parts of the two bones were rough, projecting points 
on one fitting into depressions on the other, thus strongly 
suggesting the beginning of a process of anchylosis. 
Bone 2 of Esox thus has the same general relations to the 
adjoining bones and parts of the skull that each half of the sin- 
gle ethmoids of Amia and Salmo have, the relation to the septo- 
maxillary in Amia alone excepted. I, therefore, consider the two 
bones together of Esox as the probable homologue of the single 
bones of Amia and Salmo. The only other supposition possible, 
apart from that made by Huxley, is that each bone in Esox is the 
homologue of the posterior process of the premaxillary of Amia ; 
a supposition which, from the different relations of the two bones 
to the frontals in their respective fishes, seems much less proba- 
ble. That there should be two ethmoid bones in Esox instead of 
one, as in Amia, seems to be sufficiently accounted for by the fact 
that the lines of sense organs to which the bone seems to be 
related, in Esox, are longitudinal in their general arrangement 
and not transverse. If the two bones of Esox are parts of a 
dermal ethmoid bone of that fish, instead of parts of the pre- 
