SEC. IV ANA TOMY OF BIRDS 237 



basisphenoidal rostrum, may like the latter be thickened by bearing 

 its share of the parasphenoidal splint. Oftener, however, this lower 

 border slopes upward and forward, from the sphenoidal base to the 

 roof of the skull about the site of the craniofacial suture ; and 

 usually the septum is incomplete, having a membranous fenestra 

 somewhere near its middle (Fig. 70, iof). Along the upper border 

 of the mesethmoid plate, or just in the crease between it and the 

 overarching frontal, may usually be seen a long groove, which, be- 

 ginning behind at the olfadm-y foramen of the brain-box, conducts 

 the thence -issuing olfactory nerve to the nasal chambers. Some- 

 times there is another such groove, from a foramen near by in 

 the sphenoidal parts, which similarly traces the course of the 

 ophthalmic (first) division of the trifacial nerve. Occasionally, as 

 in the fowls, the two halves of the frontal bone separate a little at 

 the extreme forehead, allowing the mesethmoid plate there to come 

 up flush with the outer surface of the skull. 



In some birds, as the low ostrich, for example, the original 

 mesethmoidal cartilage-plate does not nick apart into orbital and 

 nasal moieties, but ossifies as a continuous sheet of bone, dividing 

 right and left halves of the skull far towards the point of the beak 

 (see Fig. 75, beyond R to Pmx). A nasal septum, separated from the 

 orbital septum, may persist to ossify ; forming, as in the raven, a 

 vertical plate separate from all surroundings, and liable to be mis- 

 taken for a free vomer (see Fig. 79, where the reference line v goes 

 to it, instead of to the truncate vomer) ; or, as in many birds, a 

 plate variously ankylosed with its surroundings. But these forma- 

 tions, as well as the various twrhinal (Lat. turbo, a whorl) scrolls and 

 whorls formed in this part of the skull, belong rather to the organ 

 of smell than to the skull proper. 



The Cranial Bones proper are all those thus far described, 

 excepting the nasal ossifications just noted, which belong to the first 

 preoral arch ; and the stapedial parts of the ear, which belong to 

 the hyoidean apparatus (second postoral arch). Intermediate in 

 some respects between the proper cranial bones and 



The Facial Bones proper is the Vomer. — By " facial bones," 

 as distinguished from "cranial" bones, is meant the entire bony 

 scaffolding of the upper and lower jaws, and of the tongue, — 

 parts developed in the preoral or maxillary, and first, second, and 

 third postoral, or mandibular, hyoidean proper, and branchial, 

 arches. 



The Vomer (Lat. vomer, a ploughshare ; Figs. 62, 63, 75 to 80, v) 

 was considered, by those who held the vertebral theory of the skull, 

 to be the body of the foremost (fourth from behind — the basioc- 

 cipital, basisphenoid, and presphenoid being the other three) cranial 

 vertebra. So far from having any such morphological significance. 



