THE ENTIEE SKULL 507 



VARIATIONS IN THE SKULL. 



The size and shape of the adult skull can be obtained by straight 

 measurements, curved measurements, angular measurements, and meas- 

 urements of capacity. 



(1.) Straight measurements are made by taking the shortest dis- 

 tance between two points. When these points are upon the same 

 aspect of the skull, straight compasses can be used; if, however, they 

 lie on different aspects, curved calipers or sliding calipers, graduated 

 in millimetres, must be employed. 



(2.) Curved measurements are taken with a small metal tape- 

 measure applied directly to the surface and made to follow its undu- 

 lations. The horizontal and vertical transverse circumferences of the 

 skull are sometimes measured in this way. 



(3.) Angular measurements may be taken directly with the instru- 

 ment known as a protractor, or the angle may be fixed by compasses 

 and then measured on the protractor. Compasses of different sizes 

 and shapes can be easily made by joining two narrow strips of card- 

 board at one end by a metal eyelet. If the skull has been bisected, 

 some of the angles can be traced upon transparent paper. In this 

 way can be determined the angle which the plane of the foramen 

 magnum forms with the cranial base, the inclination of the vertical 

 plate of the occipital or of the front of the face, and the angle formed 

 at the anterior end of the anterior sphenoid by lines drawn from the 

 basion and the premaxillary alveolar point. 



(4.) The capacity of the cranial or nasal cavity can be obtained by 

 measuring in a graduated glass the amount of fine shot it takes to fill 

 it. Before filling the cavity the larger foramina must be closed. 



In the following table I have given only straight measurements 

 and such as are not difficult to obtain. They cover the length, breadth, 

 and height of the entire skull, taken in different regions and between 

 different points ; also the diameters of the nasal, orbital, zygomatic, 

 and auditory openings ; the length of the parts of the alveolar borders, 

 the diameters of the hard palate, and the distance between fixed points 

 on the cranium and the face. From the data here presented almost 

 any index can be constructed. For example : if we wish to know the 

 breadth of the skull in terms of the length, it can be obtained from 



, , . , maximum intertemporal width X 100 



the breadth index, or . . 



premaxillary-inion length 



