UPON THE SERIES OP PREHISTORIC CKANIA. 677 



portion at all approaching equality with the part anterior to it is 

 a retention of infantile proportions, and ])ro tanto a sign of 

 inferiority. 



Mutatis mutandis a comparison of the skulls of the anthropo- 

 morpha leads us to a similar conclusion. In those apes though the 

 lobule of the marginal convolution and the parietal eminence cor- 

 responding to it are only faintly marked ; and, though the Asiatic 

 Orang is often less dolicho-cephalous than its African allies ; still 

 the primitive centre of ossification of the parietal bone which may 

 be supposed to hold the same relation to the subjacent brain 

 which the homologous area in the human skull is wont to do, 

 divides the bone, in all of these Simiadse, into two much more 

 nearly equal segments than is usually the case in the adult human 

 subject. 



Thus from the four points of view furnished by considering their 

 irrigation, their histological structure, their relative activity as 

 indicated by their greater amenability to the incidence of disease, 

 and their comparative anatomy, the anterior parts of the brain of 

 which we have been treating can be shown to be superior in 

 importance to those which lie posteriorly to them. The convolu- 

 tions which are curtailed in the posterior part of a brain with 

 its anterior segments relatively large are those which underlie 

 that zone of the skull which is interposed between parallel 

 lines drawn over the parietal tuberosity and over the line of the 

 lambdoid suture. Hence the importance of the two craniographical 

 peculiarities, viz. the posterior position of the parietal tubera 

 (p. 637 supra) and the vertical dip of the posterior half of the bone 

 (p. 638 suiyra ibique citata) so characteristic of the brachy-cephalic 

 skull, and so clearly indicative of a brain, ^^ro tanto and ceteris pari- 

 bus, favourably conditioned and advantageously constituted. And 

 the rationale of a third craniographical distinction, that, namely, 

 which is given in the ' Antero-posterior Index ' (p. 563 supra), lies 

 in its furnishing us with a more or less exact numerical expression 

 of the relative extent of the more favourably conditioned segments 

 of such brains. The average antero-posterior index of the dolicho- 

 cephalic skull as obtained from the measurements, given with the 

 descriptions, of the small number of ' Silurian ' skulls figured in this 

 book, is 47 as against 52 for the average of the brachy-cephalic 

 ' Cimbric ' skulls, also figured here ; and this disadvantageous pro- 

 portion is only reduced by a fraction amounting to \ when we 

 compare the average obtained from six other prehistoric Silurian 



