SOCIETY OP THE UNIVERSITY OP ABERDEEN. 181 



closure of the cranial sutures. I do not think, however, that this can 

 be regarded as a direct cause of the synostosis, for the sutures some- 

 times close as early as thirty-five, or even earlier, at an age when the 

 individual is still vigorous, and there is no reason to suspect a falling 

 off or lowering of the general blood pressure. 



Further, it might be thought that the cause of the gradual 

 closure of the cranial sutures, which takes place after forty, was to be 

 found in the general tendency, which exists in old age, towards ossifi- 

 cation of fibrous and cartilaginous structures, such as the cartilages 

 of the ribs and larynx. The sutures, however, sometimes remain 

 open in extreme old age, e.g., Specimen 368, B. Davis, Col. R.C.S. 

 Eng., cet. 112 ; and we have no evidence that this tendency towards 

 ossification is in abeyance in these particular subjects, the skulls of 

 whom often show marked senile changes, such as absorption of the 

 alveolar processes of the upper and lower jaw bones. It cannot be 

 argued, therefore, that the persistence of the sutures in these people 

 is attributable to a greater vitality and a general postponement of 

 changes which normally take place at an earlier age, since the skulls 

 show all the usual signs of old age, with the exception of the closure 

 of the sutures. 



A consideration of the skull represented in Plate XII., Fig. 1, 

 appears to be in favour of increased intracranial pressure having 

 some influence in keeping the sutures open. In the figure it will 

 be noticed that one-half of the coronal suture, the left, has become obli- 

 terated, and that the left side of the skull in the frontal region is smaller 

 than the right ; it will also be noticed that the interfroutal suture has 

 persisted. Now the persistence of this suture might be thought to 

 have been compensatory, for it would have allowed an increase in the 

 width of the frontal bone to take place, which would have compen- 

 sated for the diminution in the longitudinal diameter on the left side, 

 caused by synostosis of the left half of the coronal suture. In cases 

 in which the metopic suture has not persisted the deformity of the 

 frontal region is more marked. The skull shown in Fig. 1 also 

 shows a persistent metopic suture, which is associated with a synos- 



