84 THE SKULL AS A WHOLE. 



Inion (I). The external occipital protuberance. 



Opistliion. The middle of the posterior margin of the foramen magnum. 



Basion (B). The middle of the anterior margin of the foramen magnum. 



Pterion (Pt). The region, near the anterior part of the temporal fossa, where the great 

 wing of the sphenoid, the squamous, the parietal and the frontal bones approach each other, 

 the exact disposition, however, varying in different individuals. In the most common 

 condition the parietal and great wing of the sphenoid meet and form a short horizontal, 

 suture ; but it sometimes happens that these two bones are separated by the junction of the 

 frontal and squamous, giving rise to a vertical fronto-temporal suture, generally continuing the 

 line of the coronal suture. The latter form is especially frequent in some of the lower races of 

 mankind, and is the rule in the gorilla and chimpanzee. There is often a small "Wormian bone 

 in this situation, the cpipteric bone of Flower, and many cases of the occurrence of a fronto- 

 temporal suture are attributable to the union of this piece of bone with the squamous or frontal. 



Stephanion (St). The point where the coronal suture crosses the temporal line. 



Asterion (As). The point where the lambdoid, parieto-mastoid and occipito-mastoid 

 sutures meet. When a separate interparietal bone is present the suture dividing it from the 

 supraoccipital runs transversely from asterion to asterion, which will in that case be the 

 meeting point of four sutures. 



Auricular point. The centre of the orifice of the external auditory meatus. 



The circumference of the cranium (horizontal) is taken in a plane passing anteriorly 

 through the ophryon, 1 and posteriorly through the occipital point (fig. 84, Op 0). This may 

 exceed to a slight degree 550 millimetres (2T7 inches) or it may be as low as 450 mm. 

 (17*7 inches). The average in the adult European male is 525 mm., in the female 500 mm. 

 For comparison of the relative development of the anterior and posterior portions of the 

 cranium, the preauricular part of the circumference is divided from the postauricular part by 

 a line on each side passing from the auricular point to the bregma (auriculo-bregmatic line). 



The length of the cranium (maximum) is measured from the most prominent point of the 

 glabella to the occipital point (fig. 84, Gl 0), and this is made the standard = 100. The 

 breadth (maximum) is the greatest transverse diameter of the cranium above the supramastoid 

 ridges, measured perpendicularly to the median plane. The proportion of the latter to the 



length ( ) is the index of breadth or the cephalic index. Skulls with a 



V length / 



breadth-index above 80 are brachrj cephalic, from 75 to 80 mesaticephalie, and below 75 dolicho- 

 cephalic. 



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

 of this to the length, calculated in the same way, is the index of height. It is subject to less 

 variation than the breadth-index ; in some cases, especially in dolichocephalic skulls, it 

 exceeds, but more frequently it falls below that index. 



Breadth- Height- 

 index, index.* 



Mongolians of Siberia and Central Asia . 88 73 



Andaman Islanders ..... 82 77 



Chinese .-.';-.*.'. .. 79 75 



English . . ...;.. 76 71 



Native Australian . . . . . 71 71 



Fiji Islanders . . . . . . 66 74 



For a more accurate determination of the form of the cranium other measurements are 

 taken, such as the transverse circumference, passing through the auricular point on each side 

 and the bregma above ; the longitudinal arc from the nasion to the opisthion, with its 

 subdivisions into frontal, parietal and occipital arcs ; transverse arcs from the posterior root 

 of the zygoma immediately above the auricular point of the one side to the other, across the 

 most prominent parts of the frontal, parietal, and occipital bones respectively. The antero- 

 posterior curve of the roof may also be indicated by a series of radii from the basion to the 

 centre of the frontal bone, the bregma, the vertex and the lambda. Other features again are 

 not capable of being expressed in terms of direct measurement, and must be described in each 

 case ; for example, the form of the transverse arch of the cranium, which in the best shaped 

 skulls is full and rounded, while in some races, notably in the Australian, the line of the 

 sagittal suture is elevated, and the surface on each side flattened or even somewhat depressed, 

 making the calvaria roof -shaped ; and this condition, combined with great prominence of the 

 parietal eminences or of the temporal lines, gives the skull, when viewed from behind, a 

 markedly pentagonal figure. The degree of complication and fusion of the sutures, the 

 amount of projection of the glabella and of the inion, and other variable points, maybe stated 

 according to tables furnished by Broca in the work referred to below. 



1 Some anthropologists measure the circumference over the glabella (Turner, Schmidt). 

 8 In these examples, which are taken from the Catalogue of the Museum of the Eoyal College of 

 Surgeons, the indices are calculated from the ophryo-occipital length. 



