THE OSTEOLOGY OP AMIURUS CATUS. 277 



the premaxillse. 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 pa,rasphenoid, vomer and 

 premaxillce ; laterally with the ectethmoids. 



14. Ectethmoids, (PI. II., Figs. 1 & 2, EEth; Fig. 2, Pfr.) 



Are the latei^al ossifications of the ethmoidal cartilage. They are 

 very deeply grooved on the inner surface for the olfactory nerves, 

 opening antorioi-ly by a large foramen, through which the nerves pass 

 to the olfactoiy organ. Laterally the bone is produced into a strong 

 slightly curved process, the a,ntorbital 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 R. ophthalmicus 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 meselhmoid 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 nasal 

 and the adnasal, on each side, and the extremity of the antorbital 

 process is in relation to the anterior ossicle of the infraorbital chain. 



15. Vomer, (PI. II., Fig. 2, Vo.) 



Is a nail-shaped bone, i.e., 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-orbit als. 



Extending fi'om the frontals downwards behind the orbit, and be- 

 low it bending and running forwards to the ectethmoid, is a chain of 

 bones lying in the dense fascia which covers the adductor uiandibulce 

 muscle. The first or superior is an almost square bone, the second 



