8o6 TRANSACTIONS OF SECTION H. 



jirea of the slfull, and gradually extends upwards upon it, so that the temporal 

 ridge reaches a much higher level than in the infant. This extension of the 

 muscular attachment proceeds gradually, and is probably not completed until 

 adult life. 



An index was constructed by takinn- a vertical line from the upper border of 

 the zygoma to a point opposite the level of the bregma as equal to 100, and 

 observing the ratio of this to a line starting from the same point below, and pro- 

 ceeding in the same direction as far as the temporal ridge. At birth the index is 

 about, Si and in the adult about G8, so that at birth the temporal muscle occupies 

 approximately the lower third of this zygomo-bregmatic line and in the adult its 

 lower two-thirds. The process is not completed at puberty, for in a girl thirteen 

 years the index was 59 6, and in another fifteen years it was 62"2. The growth 

 of the temporal muscle is associated with that of the jaws and teeth, and is 

 independent of brain growth. 



The parts of the brain situated in the mesial plane were projected outwards 

 orthogonally on to the lateral aspect of the skull. Drawings prepared in this 

 way showed that at birth the area occupied by the temporal muscle was distinctly 

 below the whole of the corpus callosum, and did not reach backwards to the level 

 of its posterior border ; whereas in the odult the corpus callosum was entirely 

 within tlie temporal region. A series of specimens, arranged according to age, 

 between infancy and adult life exhibited a gradual expansion of the temporal 

 area towards, upon, and finally above and behind the corpus callosum. During 

 this period the height of the corpus callosum maintained a fairly constant relation 

 to that of the cranium, and the rates of growth of these two structures closely 

 corresponded with each other. 



10. The Development and Adult Form of the Human Brain, 

 By Professor A. Fraser. 



11. The Significance of the so-called Accessory Dental Masses sometimes 

 found in the Upper Jaivhones. By Professor A. Francis Dixon. 



An examination of a group of young Ibo skulls from West Africa leads to the 

 belief that the small ' accessory dental masses,' which may occur in the maxilla 

 between the second premolar and the first molar, have not the important morpho- 

 logical significance sometimes attributed to them. It has been suggested that 

 these rudiments, which are fairly common in negro skulls, represent aborted or 

 vestigial premolars corresponding to the third premolars of platyrrhine apes. The 

 Ibo skulls examined do not bear out this interesting suggestion, for in them the 

 rudiments can be seen to arise as unabsorbed portions of the second milk molar. 

 In some of the specimens the actual method of their formation can be followed. 

 The origin of the rudiments explains their rather variable microscopic structure 

 and the absence, or relatively small amount, of enamel usually present. The 

 question as to why fragments of the second milk molars should be relatively so 

 frequently retained in certain races is one of considerable interest. 



12. Who Built the British Stone Circles? By J. Gray, B.Sc. 



Closely associated with dolmens and avenues in Britain, there are thre^ 

 leading types of stone circles — namely, the Dartmoor, the Aberdeenshire, and the 

 Inverness types, the simplest forms being found in the south. 



The distribution of stone circles in Britain would be simply explained if we 

 assume that the race who built them first settled in Cornwall and Devon, then 

 migrated up through Wales, Lancashire, and South-West Scotland as far as the 

 mouth of the Clyde, from thence across the midlands of Scotland to the mouth 

 of the Tay,then north along the east coast, through East Aberdeenshire, turning 



