552 



SCIENCE. 



[N. S. Vol. XVIII. No. 461. 



breadth, taken between the outer surfaces 

 of the zygomatic processes of the temporal 

 bone, is 172 mm., giving the marked 

 brachycephalic index of 88.21. The zygo- 

 matic processes, however, may reasonably be 

 objected to as indicating the true breadth, 

 and the side wall of the cranium just above 

 the line where the root of' this process 

 springs from the squamous j)ortion of the 

 temporal bone will certainly be much 

 nearer the cranial cavity. Measured in this 

 situation, the breadth of the cranium is 118 

 mm., which gives a length-breadth index 

 60.51, and thus represents the skull as 

 decidedly dolichocephalic. The transverse 

 occipital crests and the point where these 

 meet in the middle line to form the ex- 

 ternal occipital protuberance are much 

 more prominent in the male than in the 

 female gorilla, and the estimate of the 

 length of the cranium in this male gorilla 

 may be reduced to 160 mm. by selecting 

 the base of the protuberance in place of its 

 posterior extremity as the posterior end 

 measurement. This raises the index to 

 73.75, and places the skull near the mesa- 

 tieephalic group. At the anterior part of 

 the skull the prominent glabella is sepa- 

 rated from the inner table of the skull by 

 large air sinuses, so that on a median sec- 

 tion of the skull the distance from the gla- 

 bella to the nearest part of the cranial 

 cavity is 36 mm. We have here, therefore, 

 another outgrowth of the cranial wall which 

 in an examination of the external surface 

 of the skull obscures the extent of the 

 cranial cavity. Accordinglj^ the glabella 

 can not be selected as the anterior point 

 from which to measure the length of the 

 cranium, and must, like the zygomatic 

 arches and occipital protuberance, be ex- 

 cluded from our calculations if we desire 

 to determine a true length-breadth index. 

 The difficulty, however, is to select a def- 

 inite point on the surface of the cranium 



to represent its anterior end, which will be 

 free from the objections justly urged 

 against the glabella. Schwalbe suggests the 

 hinder end of the supra-glabellar fossa, 

 which he states often corresponds to the 

 beginning of a more or less distinctly 

 marked frontal crest. I have found this 

 point either difficult to determine or too far 

 back. Thus in my male gorilla the poste- 

 rior end of this fossa formed by the meeting 

 of the two temporal ridges w'as 56 mm. be- 

 hind the glabella, and only 24 mm. from the 

 bregma, while in the female gorilla the 

 temporal ridges do not meet, but there is 

 a low median frontal ridge, which may be 

 considered as bounding posteriorly the 

 supra-glabellar fossa. This point is 22 

 mm. from the glabella, and between 50 mm. 

 and 60 mm. in front of the bregma. 



I would suggest a spot in the median 

 line of the supra-glabellar fossa which 

 is crossed by a transverse line uniting 

 the posterior borders of the external 

 angular processes of the frontal bone. I 

 admit this plan is not free from objections, 

 but it possesses the advantages of being 

 available for both male and female skulls. 

 In my male skull the selection of this point 

 diminishes the length of the cranium by 25 

 mm., thus reducing it to 137 mm. The 

 breadth being calculated at 114 mm., the 

 index is 83.21, and hence distinctly brachy- 

 cephalic. The length of the cranial cavity 

 is 118 mm. and the breadth 96 mm., and 

 the length-breadth index is thus the brachy- 

 cephalic one of 81.36. 



I have given these somewhat detailed 

 references to the measurements of this 

 gorilla's skull beeaiase they show in a very 

 clear and obvious manner that from an ex- 

 ternal examination of the ski;ll one might 

 easily be misled as to the size and form 

 of the cranial cavity, and that, in order 

 to determine from external measurements 

 the proportions of the cranial cavity, skul! 



