^<'<^ GENEBAL ORNITHOLOGY. 



and abducent) which move the muscles of the eyeball; these holes being collectively about 

 equivalent to the foramen lacerum anterius of human anatomy. Parts about the optic foramen, 

 before and above, are presphenoidal (figs. 70, 71, ps) and (jrbito-spheuoidal ; but they are 

 obscure to all but the embryologist, and practically furnish no zoological cluiracters. 



The Ethmoid (Gr. rjdfioi, ethmos, a sieve ; from tlie way it is ]ierfurated in the human 

 species ; tig. G2) is the bone of the mid-line of the skull, in i'ront of the sphenoidal elements and 

 below the frontal ; it is in special relation with the olfactory nervous apparatus, or sense of 

 suiell. This is not an easy bone to " get the hang of" in birds. Keferring to figs. 66, OS, eth, 

 the student wiU see in the early embryo a high thin plate (.>f cartilage, the mesetlimoid cartUage, 

 which is developing lateral processes to fonn the convoluted walls of the nasal passages. By 

 the uprising and forth-growing of the prenasal cartilage, the mesethmoidal plate is tilted back- 

 ward, as it were, under the fi-ontal. Next, by absorption of tissue just opposite the future 

 cranio-facial suture, the plate is nicked apart, the portion in front of the nick elaborating 

 tlie nasal chambers, which usually remain cartilaginous, and the portion behind this nick 

 becoming the permanent plate, fig. 70, dh, pe, to which the name mesetlimoid or mid-ethmoid 

 is more strictly applicable. Practically, a bird's ethmoid is chiefly the inter-orbital septum, in 

 \ertical mid-line between the orbits, with such fiange-like jirocesses or lateral plates as may be 

 developed to furm an orbito-nasal septum separating the eye-socket from the nose-chamber, 

 lu general, tlie permanent ethuKiidal plate becomes nearly coincident \i'ith this orbital wall, and 

 pretty well cut off from the osseous or cartilaginous developments, wiicn any, in the nasal cavi- 

 ties. It is then fairly under cover fjf the frontal, with which, as with the sphenoidal elements 

 [losteriorly, it becomes completely fused. When this inter-orbital septum is fully developed, it 

 couipletely divides the right and left orbital cavities, and its lower horizontal border, fused 

 with the basispheuoidal rostrum, may like the latter lie thickened by bearing its share of the 

 jiarasphenoidal splint. Oftener, however, this lower border slopes upward and forward, from the 

 sjdienoidal base to the roof of the skull about the site of the cranio-facial suture; and usually 

 the septum is incomplete, haviug a membranous fenestra somi'where near its middle (fig. 70, 

 iof). Along the upper border of the mesethmoid plate, or just iu tlie crease between it and 

 the overareliiug frontal may usually be seen a long groove, which, beginning behind at the 

 olfactory foramen of the brain-box, conducts tlie thence-issuing idfactory nerve to the nasal 

 cliambers. Sometimes there is another such groove, from a similar foramen near by in the 

 sphenoidal parts, which similarly traces the course of the (jphthaluiic (first) ilivisiou of the tri- 

 facial nerve. Occasionally, as iu tlie 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 ostricli, for example, the original mesethmoidal cartilage-plate 

 <loes 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 fio-. 75, beyond 

 A' to Fiiix). A nasal septum, separated from the orbital septum, may persist to ossify ; form- 

 ing, as in the raven, a vertical plate separate from all surroundings, and liable to be mistaken 

 lor a free vomer (see fig. 79, where the reference line r goes to it, instead of to the truncate 

 vomer) ; or, as in many birds, a plate variously ancliylosed with its surroundings. But these 

 formations, as well as the various iurbinal (Lat. turbo, a Avhorl) scrolls and whorls formed in 

 this part, of the sliull, belong rather to the organ of smell tlian to tlie skull ]iroper. 



The Cranial Bones proper are all those thus far described, excepting the nasal ossifica- 

 tions just noted, which belong to the first jire-oral arch ; and the stapedial parts of the ear, 

 which belong to the liyoidean apparatus (second post-ora^i arch). Intermediate in some 

 ii'spects between the propier cranial bones and 



