THE SKULL AS A WHOLE 



147 



The height is usually measured from the basion to the bregma, and the proportion of height 



, (height X 100) 

 to length i ,, constitutes the vertical or height index. 



In studying the face the principal points to be noticed are the proportion of its length and 

 breadth, the shape of the orbits and of the anterior nasal aperture, and the degree of projection 

 of the jaws. 



The length of the face may be measured from the ophryon or nasion to the chin, or, if the man- 

 dible be wanting, to the alveolar point; while its width is represented by the distance between the 

 zygomatic arches. By comparing the length with the width of the face, skulls may be divided 

 into two groups dolichofacial, or leptoprosope (long-faced), and brachyfacial, or chemoprosope 

 (short-faced). 



The orbital index signifies the proportion which the orbital height bears to the orbital width, 

 thus: 



orbital height X 100 

 orbital width 



The naftal inde.r expresses the proportion which the width of the anterior nasal aperture bears 

 to the height of the nose, the latter being measured from the nasion to the lower margin of the 

 nasal aperture, thus: 



nasal width x 100 

 nasal height 



The degree of projection of the jaws is determined by the gnathic or alveolar index, which 

 represents the proportion between the basialveolar and basinasal lengths, thus: 



basialveolar length X 100 

 basinasal length 



The following table, modified from that given by Duckworth, illustrates how these different 

 indices mav be utilized in the classification of skulls. 



Surface Form. The various bony prominences or landmarks which are to be easily felt and 

 recognized in the head and face, and which afford the means of mapping out the important struc- 

 tures comprised in this region, are as follows: 

 , 1. Supraorbital arch. 



2. Internal angular process. 



3. External angular process. 



4. Zygomatic arch. 

 o. Mastoid process. 



6. External occipital protuberance. 



7. Superior curved line of occipital bone. 



8. Parietal eminences. 



9. Temporal ridge. 



10. Frontal eminences. 



1 1 . Superciliary ridges. 



1 2. Xasal bones. 



13. Lower margin of orbit. 



14. Mandible. 



(1) The supraorbital arches are to be felt throughout their entire extent, covered by the eye- 

 brows. They form the upper boundary of the circumference or base of the orbits, and separate 



