SOCIETY OF THE UNIVERSITY OF ABERDEEN. 189 



larities, such as extreme complexity, or simplicity of the suture line, 

 and persistence of the sutures in old age. 



Now since growth of the bones of the skull takes place at their 

 edges, it is to be expected that premature union of sutures will be 

 accompanied by an arrest of growth of the skull in a direction at right 

 angles to the suture, and conversely that if a suture that normally 

 closes early remains open, that there will be an increased growth of 

 the bones on each side of the suture and an increase in the diameter 

 of the skull, which will be at right angles to the abnormal suture. 



That such is the case is abundantly proved by the examination of 

 skulls in which one of these two conditions is present or in which there 

 are additional sutures, such as a transverse parietal. 



A full description of the effect that premature ossification of the 

 sutures has upon the shape of the skull is to be found in an article 

 by J. Barnard Davis, on "Synostotic Crania," published in 1856 ; the 

 subject has also been studied by Virchow, who first enunciated the 

 law, that " in synostosis of a suture the development of the skull is 

 arrested in a direction perpendicular to the synostotic suture," and 

 who drew up a very complete classification of the different forms of 

 skull which arise from this and other causes. I shall, therefore, 

 merely describe a few of the more important examples of deformity 

 due to synostosis. 



Commencing with the lambdoid suture, we have obliteration of 

 one side only of this suture, causing diminution of the same side of 

 the skull, which is compensated for by a corresponding increase on 

 the opposite side ; there is thus an obliquity of the skull to which 

 the name " plagiocephaly " has been applied. The deformity is not 

 always present, however, or at any rate not in a marked degree, as in 

 specimen 98"), R.C.S. England. In this case the line of the suture is 

 distinctly visible, and it is possible that it may not have closed till 

 after the principal growth of the skull had been completed. 



Obliteration of the whole of the lambdoid suture is accompanied 

 by arrest of growth in the occipital region, with compensatory en- 

 largement in the region of the anterior fontanelle. When associated 



