70 THE SKELETON ■ 



The obelion, a little anterior to the lambda, is usually indicated by a median 

 or two lateral foramina. It indicates the spot where the sagittal suture first suffers 

 obliteration. 



Vieued from hihind, the skull appears irregularly globular; the inferior part of 

 its circumference being somewhat flattened. The limits of the flattened portion 

 are indicated bv the mastoid jirocesses. 



The centre is occui)ied by the occipital protuberance ; this, with the occipital 

 crest and the three ijairs of nuchal lines, give to the lower half a xX)ugh and uneven 

 ajipearance. The sutures in this view are the terminations of the sagittal, lamb- 

 doi(hd and, wht-n itnsent, the occipital suture. 



Tlie occipital point (fig. 90j is the most posterior part of the skull, and is 

 exactly oi)posite the o})hryon. 



The inion corresponds to the external occipital protuberance. 



The lateral a>>pect of the skull is very uneven; it presents three recesses or fossae. 

 Its irregularity is increased by the zygoma. 



The temporal fossa, semilunar in shape, is limited above by the superior 

 temporal ridgf, and below by the zygoma. 



The temporal ridge begins at the external angular process of the frontal bone, 

 and curves upwards and backwards to cross the frontal and parietal bones; it then 

 descends along the mastoid portion of the temporal bone to become continuous 

 with the upper border of the zygoma. In many skulls this ridge is double. The 

 lower ridge gives origin to the temporal muscle. The upper is the least constant; 

 it diverges from the lower ridge as it approaches the coronal suture. At the middle 

 of the parietal bone the two ridges are often ten millimetres apart. This ridge gives 

 attachment to the temporal fascia. The fossa is almost entirely occupied by the 

 temporal muscle. 



The zygomatic fossa is limited anteriorly by the zygomatic surface of the 

 maxilla; internally liy the external pterygoid plate; externally by the zygomatic 

 arch and the rannis of the mandible; and posteriorly by a line drawn from the 

 foramen spinosum to the zygomatic tubercle. The outer surface of the greater 

 wing of the sphenoid internal to the pterygoid ridge and a small piece of the 

 s(|uamosal form part of the upper boundary of the fossa. 



The chief objects of interest in this region are: — The spheno-maxillary and 

 pterygo-maxillary fissures, the pterygoid ridge on the sphenoidal wing, the 

 foramen ovale, foramen spinosum, and the articular eminence of the 

 scjuamosal. 



The spheno-maxillary fissure is horizontal in position, and lies between the 

 orbital border of tlie maxilla and the greater wing of the sphenoid; externally it is 

 completed usually by the malar; freciuently the sphenoid will join the maxilla and 

 exclude the malar bone froiu the fissure; internally it is terminated by the zygo- 

 matic surface of the orbital i)roccss of the palate bone. Through this fissure the 

 (trbital, spheno-maxillary, and zygomatic fossa? communicate. The zygomatic fossa 

 lodges the temporcd, external pterygoid, and internal pterygoid muscles. 



The pterygo-maxillary fissure forms a right angle with the preceding. It is 

 situated between the maxilla and the anterior border of the pterygoid process of the 

 s]»henoid. At its lower angle the external pterygoid plate occasionally articulates 

 with theniaxilla. The pterygo-maxillary fissure leads from the zygomatic fossa 

 directly into the spheno-maxillary fossa, a small space shaped like an inverted 

 jtyramid, situated l)etween the maxilla and the roots of the pterygoid processes. 

 The roof of this fossa is formed by the under surface of the greater wing of the 

 s]»hen()i(l. The anterior boundaries are a small portion of the zygomatic surface of 

 the maxilla and the orbital process of the palate; posteriorlv it has the roots of the 

 pterygoid i>rocesses, and the lower part of the orbital surface of the greater wing of 

 the sphenoid; and internally the vertical ])late of the palate bone. The apex of the 

 l)yramid leads into the posterior palatine canal. The inner w\all presents the 

 spheno-palatine foramen wliidi leads into the nasal fossa. The ])osterior wall 

 has three o])enings in the following order, from without inwards, and from al)ove 

 downwards: the foramen rotundum, Vidian canal, and pterygo-palatine canal. 

 Anteriorly it communicates with the orbit by the spheno-maxillary fissure; 

 and externally the- pterygo-maxillary fissure "leads into the zvgomatic fossa. 



