[CAMERON] THE HUMAN SKULL 177 



worth^ records 138 as the average in two European skulls examined 

 by him. The writer^ recently reported 151 as the measurement of this 

 angle in two New Hebridean crania, which might thus be said to 

 represent the intermediate evolutionary phase between the anthro- 

 poids and the white races of modern mankind. 



V. Microcephaly 



The evolution theory possesses one very effective means of 

 support in the shape of the doctrine of reversion. That is to say, if 

 man has a definite ancestral tree, one ought to be able to prove the 

 existence of this ancestry by occasional reversions or "throw backs" 

 to one or other of the evolutionary stages situated lower down the 

 stem. In this connection, the writer has been for many years interest- 

 ed in the extraordinary condition termed microcephaly.^ Now there 

 are two diametrically opposed theories in existence regarding the 

 causation of this phenomenon. One of these is that it is due to prema- 

 ture synostosis of the sutures of the skull, which accordingly imprisons 

 the growing brain, thus preventing any further expansion in the size 

 of that organ. The other theory is that the fault lies entirely with 

 the brain, which simply ceases to develop beyond a certain evolution- 

 ary stage. The protective skull has then to follow suit, and conse- 

 quently becomes synostosed. After a careful study of all the facts 

 relative to these theories, and they are too many to recount in this 

 brief space, the writer is convinced that the second theory is the cor- 

 rect one. Thus one fact already strongly emphasised by the writer 

 in Section III is again brought into prominence and it is this, that one 

 cannot study the evolution of the skull and the brain apart from one 

 another. After all, the cranium is merely the protective capsule round 

 the brain exactly in the same way that all other viscera throughout 

 the body possess their investing sheaths. As a result it is reasonable 

 to expect that if the contents expand, then the capsule must accom- 

 modate itself to this expansion accordingly. Thus the main support 

 to the second theory, which proves its accuracy, is that it is founded 

 on sound evolutionary and embryological principles. Moreover, 

 Sollier"* has clinched the matter by demonstrating that the brain in 

 microcephaly exhibits a very primitive arrangement of its sulci and 

 convolutions. Therefore, microcephaly is not a pathological condi- 

 tion. It is a normal occurrence, one of the occasional hints in fact, 



' op. cit. 



2 op. cit. 



^ See The Canadian Magazine, Oct., 1917. 



* Twentieth Century Practice of Medicine. Vol. XII, p. 275. 



