440 



T)K MATTHEW YOUNG. 



sphenoid axis as above described, the other a line drawn from the basion to the 

 opistliion and lying in the plane of the foramen magnum ; in other words, the angle 

 lies between Cleland's "middle base" and "posterior base." To some extent the 

 alteration in the magnitude of this angle may be considered as indicative of changes 

 in the slope of the plane of the foramen magnum. 



A. Spheno-Ethmoidal Angle. 



In the present series of 98 male skulls under examination it was found that 

 this angle had a range of variation from 136° to 170°, and that the mean value was 

 152'35° ; the S.D. was 6'58 and V. was 4'32. For 75 skulls measured according to 

 Turner's direction the angle ranged in value from 133° to 162°, with a mean value 

 of 14772° ; the S.D. was 6'14 and the V. was 4'15. Turner's mean for 5 skulls in 

 his series was 140° ; so that if my results are truly comparable with those of Turner, 

 the anterior base of the former series is not on the average so much flexed on the 

 middle base as that of the latter. 



For the spheno-ethmoidal angle Duckworth (54) gives the following values : — 



231° 

 172° 

 202° 

 158° 

 168° 

 153° 

 138° 



Dog . . 



Cercopithecus monkey 

 Simia 

 Simiidse | Gorilla . 



.Chimpanzee . 



Tj • • -i (Aboriginal Australians (average of 2) 

 riommidaes & \ 



lEuropeans (average of 2) 



The number of individuals in the above table is, of course, quite insufficient, but 

 so far as the data go it would appear that, while the mean angle for the Scottish 

 series is less than a degree below that of the Australian aboriginal, the range of 

 variation of the angle is so great that it includes values higher than those given 

 for the gorilla and chimpanzee, and even attains a value less than 2° below that 

 given for the cercopithecus monkey, which is very expressive of the great degree 

 of variability in the extent of flexion in the cranio-facial axis even in a homo- 

 geneous series. 



A reasonable explanation for the well-marked variation in the above angle is some- 

 what difficult to find even with the evidence supplied by such a long series of skulls. 



At first sight it seemed probable that a long basi-nasal chord would be associated 

 with a wide angle, and specimens are obtainable from the series, e.g. fig. 16, illustrat- 

 ing this. On the other hand, fig. 17 shows that it is possible to have another specimen 

 with a basi-nasal length little diminished from that shown in the former figure, but 

 with the angle diminished to the extent of 34°. Figs. 18 and 19 show two skulls 

 with approximately equal basi-nasal and glabello-occipital lengths, but with spheno- 

 ethmoidal angles differing by more than 20°. 



