. Birds: the elements of ornithology . e foramen. The nerves of smellpass forwards under the roof of the orbits, through a foramenin front of each orbit between the median and lateral aperture is the olfactory foramen. A thiTd important * Their distinctness and the essential distinctness of different partsof the roof and other portions of tlie skull is known from their separatecondition in the skulls of very young birds and of other animals. THE INTBENAL SKELETON. 183 foramen, called, the foramen ovale^ ia pierced in the. transmits the third branch of the fath pair
. Birds: the elements of ornithology . e foramen. The nerves of smellpass forwards under the roof of the orbits, through a foramenin front of each orbit between the median and lateral aperture is the olfactory foramen. A thiTd important * Their distinctness and the essential distinctness of different partsof the roof and other portions of tlie skull is known from their separatecondition in the skulls of very young birds and of other animals. THE INTBENAL SKELETON. 183 foramen, called, the foramen ovale^ ia pierced in the. transmits the third branch of the fath pair of nerves. Beneath the sphenoid behind its rostrum is the opening of apassage called the eustachian tube or canal—which bifurcates asit passes backwards to the bony cavity of each ear; but thetwo tubes may open separately on the under surface of the back, on either side is the opening of another canal,which transmits an important blood-vessel called the carotid *artery. These parts are bounded below by the bony plates. a, Surangular bone of mandible; ar, articular bone; d, dentary; f, frontal;i, jugal; I, lachrymal ■„ me, median ethmoid; mx, maxillary bone; p,parietal; pf, post-frontal process; pt, pterygoid bone ; px, premaxilla;5, quadrate bone; gj, quadrato-jugsd; sq, squamosal; v, vomer. called basi-teraporals. The nerve which moves the tongue,the ninth or hypoglossal nerve, passes out through the basi-occipital, and the nerve called vagus makesi its exit from theskull more externally and a little anteriorly to the Alittle more anterior still, is that hinder opening of a canal forthe carotid artery just mentioned. Part of the interorbital septum and more or less of themedian partition between the nostrils may remain gristly orcartilaginous. In the very young condition the skuU is entirelyformed of membrane and cartilage, and whien the bones beginto form they are numerous and distinct, but they mostly soon * See below, p. 217. 184 ELBMBNTS OP OE
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