THE BONES OF THE HEAD 13I 



of the orbital plate of the superior maxilla. It is situated on the 

 inner wall of the orbit, where that wall meets the floor, and its 

 direction is antero-posterior. It is parallel to the fronto-ethmoidal 

 suture, and is a harmonic suture. 



Schindylesis. — There are only a few examples of this variety of 

 synarthrosis, or immovable joint, in the skull. These are as follows : 

 (i) The articulation between the inferior border of the vomer and 

 the cleft which Hes along the nasal crests of the palatcd plates of 

 the superior maxillary and palate bones; (2) the articulation 

 between the rostrum of the sphenoid and the cleft on the superior 

 border of the vomer between the two thick, everted alae ; and (3) the. 

 articulation between the inferior border of the perpendicular plate 

 of the ethmoid with the narrow cleft on the anterior border of the 

 vomer. 



Gomphosis. — ^This variety of synarthrosis is illustrated in the 

 impaction of the fangs of the teeth within the alveoh of the superior 

 and inferior maxiUae. 



Synehondroses. 



The following are examples of this temporary form of synar- 

 throsis : 



Synchondrosis Spheno-Occipitalis. — This is situated between the 

 posterior surface of the body of the sphenoid and the anterior 

 surface of the basilar part of the occipitcd bone. 



Synchondrosis Petro-Occipitalis. — This is situated between the 

 jugular impression on the inferior surface of the petrous part of 

 the temporal bone and the extremity of the jugular process of the 

 occipital. 



Synchondrosis Spheno-Petrosa. — This is situated between the 

 posterior border of the great wing of the sphenoid and the anterior 

 part of the petrous portion of the temporal bone. 



There are also intra-occipital and intra-sphenoidal synchondroses 

 until the ossification of these bones is completed. 



I. The Posterior Region of the Skull. 



The posterior region (norma occipitalis) is formed by the posterior 

 parts of the parietal bones and the upper or interparietal division 

 of the tabular part of the occipital. It is limited above by a line 

 connecting the parietal eminences, and below by the superior 

 curved lines of the occipital, whilst laterally it is limited by a 

 line connecting the parietal eminence w'ith the lateral angle of the 

 tabular part of the occipital. A little above the centre it presents 

 the lambda, which is the place where the sagittal meets the lambdoid 

 suture in the situation of the posterior fontaneUe of early hfe. 

 Radiating from the lambda there are three sutures. One passes 

 upwards and forms the posterior part of the sagittal or interparietal 

 suture. The other two, diverging, pass out%vards and downwards, 

 and form together the lambdoid or occipito-parietal suture. About 

 I inch above the lambda, at either side of the sagittal suture, is the 



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