442 



DR MATTHEW YOUNG. 



for aboriginals of Australia (average of 7) an angle of 92° 20', and for Europeans 

 (average of 2) an angle of 75° 30' ; but it is obvious that the latter value cannot be 

 accepted as an approximate mean value for European skulls. 



The spheno-maxillary angle, as defined by Huxley, and slightly different from 

 the above angle, was utilised by him to classify crania into orthognathous if the 

 angle was less than 95°, and prognathous if it was more than 95°. The size of the 

 angle is, to a certain extent, an index to the degree of prognathism ; but, as Turner 

 points out, it is influenced, as is also the spheno-ethmoidal angle, by the variation in 

 the slope of the basi-occipito-sphenoid axis. 



In the series of 98 sagittal tracings under examination I marked in the Frankfurt 

 horizontal line, and, this being intersected by the basi-occipito-sphenoid axis, I 



Fig. 21. — Impression of median sagittal section of skull 

 No. 26, series F ; cubic capacity, 1040 c.c. 

 Spheno-ethmoidal angle, 167°. 

 Spheno-maxillary angle, 90°. 

 Foramino-basilar angle, 143°. 



Fig. 22. — Impression of median sagittal section of skull 

 No. 21, series F ; cubic capacity, 1000 c.c. 

 Spheno-ethmoidal angle," 156°. 

 Spheno-maxillary angle, 88°. 

 Foramino-basilar angle, 153°. 



measured the angle between the two, which gave me the change of slope of the above 

 axis to the Frankfurt horizontal plane. This angle I have named the "y" angle in 

 my tracings. It was found to vary in the series from 29° to 52° ; the S.D. was 4"14 

 and the V. was 10*29. 



From the above range of variation, i.e. 23° in the slope of the occipito-sphenoid 

 axis in a uniform series, it is quite evident that this factor cannot be neglected in 

 the general statement that the magnitude of the spheno-maxillary angle may be used 

 unreservedly as a criterion for the degree of prognathism. 



From the supposed constancy of the somewhat similar angle between the basi- 

 nasal line and the Frankfurt horizontal plane, Thomson and M'Iver (55), who found 

 that in 38 skulls it varied from 22° to 34°, with a mean value of 27°, made use of it 

 in a scheme for the measurement of prognathism. Furst (56), however, found that 

 the angle possesses such a degree of variation that a constant size cannot be 

 ;i<<epted for it. 



