228 



THE CRANIA OF THE SIMIIDAE (PRIMATES) [SECT. A 



of basal elements becomes more marked as we descend the series, 

 and that long before we leave the Primates the straightness is 

 interrupted, and that in the following way. 



If we suppose the central part of the series of bones, viz. the 

 sphenoid and the basi-occipital (B. Pr., Fig. 150), to be the more 

 fixed portion of the base, then we can describe the condition 

 obtaining in the human skull as one in which the ethmoidal 

 element (Pr. N., Fig. 150) is bent, or inflected, strongly downwards 

 from the anterior end of this fixed portion. And proceeding 

 to the simian skull, the appearance is such that the ethmoidal 

 element is bent downwards to a smaller degree, so much less in 

 fact that it is almost in line with the fixed portion as just defined. 

 Lastly, when w,e examine the skull of a lowlier primate form such 

 as Mycetes (Cebidae), the condition is such that the ethmoidal 

 line is so to speak reflected, or bent, not downwards, but upwards 

 (as in the Carnivora; cf. Figs. 150 c and 152) with regard to the 

 more fixed element. 



We may now turn our attention to the region of the foramen 

 magnum. This is placed in 

 the simian skull rather at the 

 junction of the posterior and 

 inferior aspects of the cranium, 

 than frankly on the inferior 

 aspect as in Man. 



A line (Op. B., Fig. 151) 

 drawn from the anterior to the 

 posterior median point on the 

 margin of this foramen repre- 

 sents what is described as the 

 " plane of the foramen mag- 

 num " (Cleland called it the 

 " posterior base of the skull " 

 but the former name may be 

 retained for the moment) ; the line representing this plane (and 

 therefore the plane itself), will be found to be inclined to the 

 spheno-basilar or "fixed" portion of the base (B. Pr., Fig. 151), in 

 such a way that the angle between the two is salient down- 

 wards (cf. Figs. 150 A and 151): moreover in the Simiidae 



Fig. 151. Cranium of an aboriginal 

 native of Australia (Hominidae) bisected in 

 the median sagittal plane. N. Pr. represents 

 the anterior or ethmoidal portion of the 

 cranial base; Pr. B. is the middle or basi- 

 occipito-sphenoidal portion; B. Op. repre- 

 sents the plane of the foramen magnum. 



