180 PROCEEDINGS OF THE ANATOMICAL AND ANTHROPOLOGICAL 



considerable separation of the parietal bones with widening of the 

 interparietal suture. Now since premature synostosis of the metopic 

 suture does not always cause trigonocephaly, it is evident that there 

 must be some other factor in its causation, and it might even be 

 argued that closure of this suture in cases of trigonocephaly was the 

 result of a failure in the development of the frontal lobes of the brain, 

 rather than that the arrest in the development of these lobes was 

 secondary to closure of the suture. I am inclined to think, however, 

 that as scaphocephaly is undoubtedly in many instances due to pre- 

 mature synostosis at the sagittal suture, that trigonocephaly is due to 

 the same condition occurring at the metopic suture, more especially 

 as the prominent ridge passing down the middle line of the frontal 

 bone in trigonocephaly corresponds to the similar median ridge or 

 keel which is frequently seen in scaphocephalic skulls. The early 

 union of the bones in these cases is generally believed to be due to a 

 pachymeningitis or osteitis occurring during intrauterine life. A con- 

 sideration, therefore, of these cases of trigonocephaly, in which the 

 cause of the synostosis of the metopic suture is believed to be patho- 

 logical, does not assist us in the search for the determining cause of 

 the closure of this suture in the normal subject. 



Synostosis of the metopic suture normally takes place before the 

 brain has attained its maximum size. Now since the remaining 

 sutures of the vault do not close till long after the brain has ceased to 

 grow, but, on the other hand, has already diminished very consider- 

 ably in size, there is obviously no correspondence in the time of the 

 closure of the cranial sutures and the time at which the growth of 

 the brain ceases. 



It must be remembered, however, that the intracranial pressure 

 after the growth of the brain has ceased is dependent on the pressure 

 of the eerebro-spinal fluid, which has been shown by Dr. Leonard 

 Hill to vary directly with the venous blood pressure in the sinuses 

 of the dura mater. 



Now it it quite possible that a diminution of this pressure of the 

 cerebro-spinal fluid may occur with the onset of old age and favour 



