ee 
THE OSTEOLOGY OF AMIURUS CATUS. 277 
the premaxille. Its posterior articular surfaces, both above and be- 
low, are very much indented, split up, in fact, into a number of very 
long osseous spicules, as in the parasphenoid and vomer, which fit 
in between corresponding spicules in the bones with which it articu- 
lates. Its articulations are :—behind with the orbitosphenoid, fron- 
tals and parasphenoid ; below with the parasphenoid, vomer and 
- premaxille ; laterally with the ectethmoids. 
14. Ecretumoips, (PI. II., Figs. 1 & 2, HHth; Fig. 2, Pfr.) 
Are the lateral ossifications of the ethmoidal cartilage. They are 
very deeply grooved on the inner surface for the o/factory nerves, 
opening anteriorly by a large foramen, through which the nerves pass 
to the olfactory organ. Laterally the bone is produced into a strong 
slightly curved process, the antorhital process, and below this is a 
roughened surface for articulation with the posterior extremity of the 
palatine. The lower and posterior surface of the antorbital process 
presents one or two foramina through one of which a branch from 
the deep branch of RF. ophthalnicus trigemini passes. The upper 
surface of the bone is irregular, and presents many foramina con- 
nected with the mucous canal system. The ectethmoids articulate 
with the mesethmoid interiorly ; the frontals and orbitosphenoids be- 
hind ; the vomer below, and the palatine externally. Their upper 
surfaces also come into relation with two membrane bones, the nasa/ 
and the adnasal, on each side, and the extremity of the antorbital 
process is in relation to the anterior ossicle of the infraorhital chain. 
15. Vomer, (Pl. Il., Fig. 2, Vo.) 
Is a nail-shaped bone, 2.¢., very much expanded in front, and ab- 
ruptly narrowed and tapering toward the posterior extremity. It 
lies below the mesethmoid and anterior portion of the parasphenoid, 
with which it interdigitates. 
Certain membrane bones, developed in connection with the mucous 
canal system, may also be described as belonging to the cranium ; 
these are the infra-orbitals, the nasals, and the adnasals. 
16. INFRA-ORBITALS. 
Extending from the frontals downwards behind the orbit, and be- 
low it bending and running forwards to the ectethmoid, isa chain of 
bones lying in the dense fascia which covers the adductor mandibule 
muscle. The first or superior is an almost square bone, the second 
