PRACTICAL CONSIDERATIONS : THE SKULL. 



241 



The inion or external occipital protuberance, which approximately corresponds 

 to the point of convergence of five sinuses (the superior longitudinal, the two lateral, 

 the straight, and the occipital), is easily felt in the mid-line behind; The superior 

 curved lines which run outward from this point indicate the muscular origin of the 

 occipito-frontalis, and hence are often the lower limit of effusions beneath the 

 aponeurosis. These ridges indicate approximately the course of the lateral sinuses, 

 which are on a line drawn from the inion to the superior border of the mastoid 

 apophysis, — i.e., to a point about 2.5 centimetres, or one inch, behind the external 

 auditory meatus. 



The asterion or junction of the squamous and lambdoid sutures is 12.5 milli- 

 metres, or half an inch, above and 18.5 millimetres, or three-quarters of an inch, 

 behind the upper level of the posterior border of the mastoid. A line from the 

 asterion to the inion is therefore also the line of the lateral sinus. 



The lambda, the junction of the lambdoid and sagittal sutures, lies in the median 

 line posteriorly about seventy millimetres, or two and three-quarters inches, above 

 the inion. In early life the posterior fontanelle is found at that point. 



Fig. 265. 



Brea-ma Biauricular line 



Stephanion 

 Inferior stephan 



Obelion 



Malar point 



Alveolar point 



Mental point 



-—Lambda 



Occipital point 



Asterion 



Gonion 

 Lateral aspect of the skull, showing the various points. (See also description on page 228.) 



The bregma, the junction of the coronal and sagittal sutures (and in childhood 

 of the frontal suture), marks the position of the anterior fontanelle, and is found a 

 little anterior to the centre of the shortest line that can be drawn over the vertex 

 between the two external auditory meatuses. 



The ptcrion is the point of junction of the temporal, sphenoid, frontal, and 

 parietal bones. It is from thirty to thirty-eight millimetres, or one and a quarter 

 to one and a half inches, above the zygoma, and the same distance behind the 

 external angular process of the frontal. It represents the position of the trunk and 

 of the large anterior branch of the middle meningeal artery. 



The zygoma can easily be traced from its anterior to its posterior extremity. 



The temporal ridges can often be felt as two curved lines, the upper one mark- 

 ing the attachment of the temporal fascia and the lower one that of the muscle. 

 They indicate the upper boundary of the temporal fossa, and often limit the spread 

 of effusions or the growth of tumors. 



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