THE INTERNAL SKELETON. 183 
foramen, called the foramen ovale, is pierced in the alisphenoid. 
It transmits the third branch of the fifth pair of nerves. 
Beneath the sphenoid behind its rostrum is the opening of a 
passage called the eustachian tube or canal—which bifurcates as 
it passes backwards to the bony cavity of each ear; but the 
two tubes may open separately on the under surface of the skull. 
Further 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 
Fig. 151. 

Sipe View or Fowt’s SKULL. 
a, Surangular bone of mandible; a7, articular bone; d, dentary ; f frontal ; 
7, jugal; 7, lachrymal; me, median ethmoid ; mx, maxillary bone; p, 
parietal ; pf, post-frontal process; pt, pterygoid bone ; pv, premaxilla; 
g, quadrate bone; qj, quadrato-jugal ; sg, squamosal ; v7, vomer, 
called “ basi-temporals.” The nerve which moves the tongue, 
the ninth or “ hypoglossal nerve,” passes out through the basi- 
occipital, and the nerve called ‘‘ vagus” makes its exit from the 
skull more externally and a little anteriorly to the former. A 
little more anterior still, is that hinder opening of a canal for 
the carotid artery just mentioned. © 
Part of the interorbital septum and more or less of the 
median partition between the nostrils may remain gristly or 
cartilaginous. In the very young condition the skull is entirely 
formed of membrane and cartilage, and when the bones begin 
to form they are numerous and distinct, but they mostly soon 
* See below, p. 217. 
