176 THE ROYAL SOCIETY OF CANADA 



wascalculated to be 146 by Duckworth/ while in the gorilla, man's near- 

 est relation amongst the anthropoid apes, the angle has become reduced to 

 125 as found by the same observer. In two Melanesian skulls recently 

 described by the writer^ it was calculated to be ninety-five and ninety- 

 seven, while in white races it is about seventy-five, that is to say it has 

 become reduced practically one half when compared with the skull 

 of the orang, and about one fifth when compared with the low Melane- 

 sian type. Thus one is even able to record a very decided difi'erence 

 between the size of this angle in the higher and the lower races of 

 modern mankind. This angular measurement appears to yield more 

 satisfactory and more constant results than the Frankfort angle and 

 also the angles devised by Camper, Welcker and others. A com- 

 parative study of Figs. 12 and 13 shows the effect of the reduction 

 of this angle upon the configuration of the facial portion of the skull. 

 It will be observed that both limbs of the angle have partaken in this 

 approximation, though of course the prosphenion-prosthion line has 

 been affected to a more marked degree. For example in the chimpan- 

 zee cranium the prosphenion-basion line is practically horizontal, 

 while in modern man it is very definitely directed downwards and 

 backwards. The most feasible explanation of this profound alteration 

 that suggests itself to the writer is, that the cerebellum, pons and 

 medulla have been as it were forced bodily downwards into the pos- 

 terior cranial fossa evidently by the backward growth of the occipital 

 lobes of the cerebrum. One important proof of this downward thrust 

 is that in lower animals the plane of attachment of the tentorium 

 cerebelli is very oblique, while in man it is practically horizontal. 

 This appears to indicate that though the main direction of growth of 

 the phylogenetic brain has been upwards, still there are evidences such 

 as this which show that there has been some development in a down- 

 ward direction as well, resulting of course in the formation of the middle 

 and posterior cranial fossse which are such marked features of the 

 human cranium. The spheno-ethmoidal angle has been devised^ to 

 show this sinking of the middle and posterior cranial fossae during 

 the evolution of the human skull, and has been found to yield very 

 interesting and consistent as well as progressive results (see Figs. 12 

 and 13). For example, the whole of the skull base in front of the 

 foramen magnum is almost in the same plane in some of the apes, e.g., 

 the chimpanzee and the orang, whereas in the higher hominidae the 

 angle has sunk from 180 down to 140 degrees or even less. Duck- 



^ op. cit. 

 ^ op. cil. 



' Huxley apparently first introduced this angle. See the Jour, of Anat. avd 

 Phys. Vol. I. 



