THE VARIOUS FORMS OF THE SKULL. fc5 



The situation and direction of the foramen magnum differ greatly, as was pointed out by 

 Daubenton, in man and the lower animals, in connection with the altered position of the axis 

 of the head in relation to that of the vertebral column. In man the foramen is placed in or 

 near the centre of the base of the skull, and its plane looks mainly down wards ; in quadrupeds 

 it is placed on the posterior surface of the skull and looks backwards ; while in the anthropoid 

 apes it is intermediate in position and direction. But even in human skulls similar differences 

 occur, though much less in degree. In the European the plane of the foramen is inclined 

 upwards anteriorly, in the Australian and Negro it is horizontal or even inclined slightly 

 upwards posteriorly. The degree of inclination requires for its determination a special 

 " occipital goniometer " designed by Broca. 



In the skeleton of the face the most striking differences are met with in the size of the 

 jaws and the extent to which they project forwards. The human skull, in comparisDn with 

 that of the lower animals, is especially distinguished by the great expansion of its cranial 

 portion and the relatively small development of the face, the latter being extended vertically 

 instead of horizontally, and thus brought downwards under the fore part of the cranium. A 

 marked prominence of the jaws constitutes, therefore, an approach to the animal type of 

 skull, and is to be regarded as a character of inferiority, particularly when it is accompanied, 

 as is often the case, by a low and receding forehead. The degree of projection of the jaws 

 beyond the cranium is most conveniently expressed by the gnathic or alveolar index of Flower, 

 which is obtained by comparing the basialveolar length (fig. 84, BA) with the basinasal length 

 (BN) = 100; skulls with a gnathic index below 98 are orthogiiathous, from 98 to 103 

 mesognathous, and above 103 prognathous. 



Gnathic Index 



English 96 



Chinese. . . . . 99 



Eskimo 101 



Fiji Islanders . . .103 



Native Australian . . . 104 



In the form of the nasal skeleton and the anterior nasal aperture variations are to be 

 recognised corresponding to the external conformation of the nose. Of these, the height and 

 width are capable of exact measurement, and the relation between the two, expressed by the 

 nasal index, becomes a character of considerable importance. The height is measured from 

 the nasion to the subnasal point (fig. 84, NS), the width is the greatest transverse diameter 

 of the anterior nasal aperture, and the calculated proportion of this to the height = 100, is 

 the index. With a nasal index below 48 a skull is Icptorhine, from 48 to 63 mesorhine, above 

 63 platyrhine. 



Masai Index. 



Eskimo ..... 44 



English 46 



Chinese ..... 60 



Native Australian . . . 67 



The form of the orbit also varies, but is a less significant character than that of the nose. 

 The orbital index is the ratio of the vertical height of the base of the orbit to the transverse 

 width = 100 ; if above 89 it is megaseme, between 89 and 84 mesoseme, and below 84 

 microscme. 



Orbital Index. 



Andaman Islanders ... 91 



Chinese 90 



English 88 



Native Australian . . . 81 



Guanches of Teneriffe . . 80 



For an account of the variations in the form of the palate and of the mandible, as well as 

 of the means of estimating the relative projection of the malar and nasal bones, and several 

 other measurements of the face skeleton, reference must be made to the special treatises. 



(For more detailed information on the foregoing subject consult Broca, " Instructions 

 craniologiques et craniometriques," 1875 ; Flower, " Cat. of Museum of Roy. Coll. Surg. of Eng.," 

 part i., 1879 ; de Quatrefages and Hamy, " Crania Ethnica," 1873-81 ; Topinard, " Elements 

 d'anthropologie generale ; " Turner, " Challenger " Reports, Zoology, x ; and Schmidt, 

 " Anthropologische Methoden," 1888. References to earlier writings of importance are given 

 in the last edition of this work.) 



IV. Irregularities of form The most frequent irregularity in the form of the skull is 

 want of symmetry. This sometimes occurs in a marked degree, and there is probably no skull 

 perfectly symmetrical. The condition which has been observed to co-exist most frequently 

 with irregular forms of skull is premature synostosis or obliteration of certain of the sutures. 



