230 THE CRANIA OF THE SIMTIDAE (PRIMATES) [SECT. A 



compare them to levers fixed at each end of a bar which serves 

 as a fulcrum to both. Further, that in the lowliest forms of 

 the Eutherian skull the conditions may be represented diagram- 

 matically by supposing each lever to be raised above the (more 

 or less) horizontally placed middle portion (see Fig. 153, with 

 which compare Fig. 152). 



We have seen that in the simian skull, both levers have been 

 depressed to a considerable extent, the anterior, ethmoidal one, 

 more than the posterior, foraminal one ; so that the diagram for 

 the simian type of skull is as represented in Fig. 154 (with which 

 compare Fig. 150 b) : 



N 



Fig. 154. 



or, since the anterior element is now the more nearly horizontal 

 one, thus (Fig. 155): 



Fig. 155. 



while finally, in Man, the condition incipient in the Simiidae has 

 been brought to a further stage, and the appropriate diagram is as 

 shewn in Fig. 156. 



It is therefore to be noticed (a), that the human skull is 

 characterized by the degree of flexion of these anterior and 

 posterior elements upon that part of the base which lies between 

 them ; (b), that the simian skull indicates this change in an 

 incipient stage, and is thus anticipatory of the human skull. 



In the foregoing account an attempt has been made to give a 

 general description only of the essential features of the cranial 

 base, and of the changes which are seen in its evolution. No 



