THE ENTIRE SKULL 465 



ridge is the stephanion. The junction of the parieto-mastoid, occipito- 

 mastoid, and lambdoidal sutures is known as the asterion. 1 



LOWER ASPECT OF THE SKULL. 



The outline of the lower surface of the skull is an irregular oval, 

 with the long axis longitudinal. The surface, in the main, is flat, but 

 the auditory bullre behind and the horizontal rami of the lower jaw 

 in front project on each side below the general surface. When the 

 lower jaw is removed the lower surface of the skull proper is visible 

 (Fig. 386). It consists of two well-marked parts, a triangular anterior 

 portion, forming the roof of the mouth, or hard palate, and a quad- 

 rilateral posterior portion, forming the base of the cranial cavity. 

 They are joined by a narrow median piece, which supports the soft 

 palate. They are further connected externally on each side by the 

 slender bowed zygomatic arches, which can be best seen on the lateral 

 view, and which are not regarded as parts of the base of the skull, 

 inasmuch as they do not form the lower wall or base of the nasal 

 and cranial cavities. A large square opening is left on either side 

 between the zygomatic arch and the true base of the skull which leads 

 upward into the orbital and zygomatic fossa?. The anterior region lies 

 upon a lower plane than the posterior region. The edges only of the 

 middle connecting region are on the same plane with the anterior 

 region ; the region itself is a forward continuation of the posterior 

 region in the form of a wide fossa, which disappears under the middle 

 of the posterior edge of the anterior region, leaving a wide, low opening 

 into the nasal chamber, subdivided in the recent state by the soft parts 

 into two channels known as the posterior nares. 



The anterior portion, forming the roof of the mouth, is triangular, 

 and is about as long as wide. The anterior angle is truncated and 

 slightly rounded ; it carries the six small incisor teeth. The slightly 

 elevated lateral margins, or alveolar borders, are directed from before 

 backward and outward, and contain the roots of the remaining upper 

 teeth, which are, on each side, the large canine, the three premolars, 

 and the single molar. Intervals, or diastemata, exist between the in- 

 cisors and the canine and anterior and posterior to the small anterior 

 premolar. The posterior end of the lateral border is the tuberosity 

 of the maxillary. The outer thirds of the transverse posterior border 



1 From (Gr.) aster, a star. 

 30 



