December 1, 1899.] 



KNOWLEDGE. 



26'; 



basi-alveolar length ((.'■., the distance from the anterior 

 margin of the foramen magnnm to a point on the alveolar 

 border of the upper jaw between the two central incisors). 

 Regarding the former as the constant, and the latter as 

 the variable, we are in this way enabled to determine the 

 gnathic or alveolar index : — 



Basi-alveolar length x 100 _ , . . -, 

 Ba-si:5asa~l length = ^°*^'° '^^'^- 



The sub-division of the resulting indices into three groups 

 is, of course, purely arbitrary. Flower classified his results 

 as follows : — When the index falls below i>8, it indicates 

 that the jaw projects but slightly. Such crania are termed 

 orthognathous, and include, amongst others, the mixed 

 European races, ancient Egyptians, Veddahs, etc. When 

 the index ranges between 98 and 103, the jaws are more 

 projecting ; this, the mesognathous group, comprises 

 Chinese, mixed Polynesians, American Indians, etc. 

 Whilst, when the index rises above 103, we have a very 

 pronounced projection of the jaws, as indicated by the term 

 prognathous applied to the group. Topinard takes 

 exception to this classification, expressing the opinion that 

 the range of Flower's mesognathous group (98-103) is too 

 wide. He would limit it to indices ranging between 98 

 and 100 or 101, which would have the advantage of 

 practically confining it to the yellow races, whilst all over 

 inn or 101 he would regard as prognathous. The reader 

 will at once appreciate what this difterence in classification 

 entails, for the French anthropologists are in the habit of 

 describing the Australians as a prognathous race, whilst 

 we in England term them mesognathous, their average 

 gnathic index being 101 (Duckworth). Whilst convenient 

 to employ, it cannot be said that Flower's gnathic index is 

 without objection, since it takes no account of the length 

 of the third side of the triangle, viz., the naso-alveolar 

 measurement, for on the length of this must depend the 

 relative projection of the two sides of the triangle, viz., 

 the basi-nasal and the basi-alveolar lengths. ! 



In no respect is the novice so apt to be misled as ' 

 in regard to this question of projection of the jaws. In i 

 handling and comparing skulls the utmost care must | 

 be exercised to place them in such a position that certain 

 definite points all lie in the same horizontal plane. 

 Nothing is easier than to convey an impression of prog- 

 nathism by tilting forward the face of an orthognathous 

 skull, whilst marked degrees of prognathism may be 

 masked by inclining the face in a vertical direction. 

 In the living this comparison of the face is much more 

 easy. The natural position of the head may be said to be 

 that in which the axes of vision of the two eyes lie in the 

 same horizontal plane. If, therefore, we place the subjects 

 under observation in the military position of " attention,' 

 with the heads in an easy position, and the eyes directed 

 toward the horizon, the slope of their faces can be satis- 

 factorily compared. In dealing with skulls we must find 

 some substitute for the visual axis, and that most com- 

 monly adopted is to place the crania in such a position 

 that a line passing from a point immediately above the 

 external auditory meatus behind, and the lower orbital 

 margin in front, falls in the horizontal plane. Fig. 3 iUus- 

 tratea this method of comparison. A glance at this figure 

 will enable the reader to satisfy himself that without some 

 such common basis of comparison it would be easy to 

 place the skulls in such positions as to lead to erroneous 

 conclusions. 



A comparison of the dental and gnathic indices reveals 

 the fact that prognathism of intermediate and pronounced 

 degree is associated with large teeth, whilst the microdont 

 races all more or less conform to the orthognathous type. 



The shape of the nose in the Uving displays remarkable 



differences, the long and narrow nose of the European 

 contrasts with the short and broad nose of the Negro, 



Fig. 3. — Shows the varying degree of projection of the Upper Jaw 

 .Skull a is pi-ognathoiis ; skull A is mesognathous; skull c is 

 orthognathous. 



whilst the form of the nose in the Australian displays a 

 very characteristic appearance, it is only necessary to 

 mention those extremes in order to draw attention to 

 the many intermediate varieties. The form of the nose 

 depends on the disposition of the bones and cartilages 

 which support it. At present, we are only concerned with 

 the former. Perhaps no feature of the skull is more 

 valuable in assisting the observer roughly to classify the 

 crania which he is examining than the form of the nasal 

 aperture. 



Fig. 4. — Shows the three types of Xasal aperture. Skull a is lepto- 

 rhine ; skull 4 is mesorhine; skuU c is )ilatTi'hiDe. 



A reference to Fig. 4 will enable the reader to appreciate for 



himself as to the typical forms there represented. Usually 



described as ')f pyriform shape, the nasal aperture varies in 



the relative proportions of its width and height. This is 



expressed by tlae nasal index, which is determined by 



employing the following formula — 



Nasal width x 100 „ , . , 



3= Nasal index. 

 Nasal height 



The nasal width corresponds to the maximum diameter 

 of the aperture, whilst the nasal height is estimated by 

 the measurement from the nasion ifronto-nasal suture) to 

 the sub-nasal point (middle of inferior edge at base of nasal 

 spine). 



The Leptorhine group includes those skulls with a 

 nasal index below 48 ; the Mesorhine between 48 and 53 ; 

 whilst the Platyrhine division comprises those crania with 

 an index above 53. Each of these three groups is typical 

 of the broad divisions of mankind into the white, the 

 yellow, and the black varieties ; thus the white races are 

 leptorhine, that is, they are characterised by a narrow 

 nasal aperture ; the Mongoloid type, if we except the 



