SOCIETY OF THE UNIVERSITY OF ABERDEEN. 187 



with in a marked degree, causing great thinning of the skull ; so that 

 the bones of the vault become translucent, or in extreme cases per- 

 forated. The general atrophy with thinning of the skull in one 

 aged specimen described by Barnard Davis was so great that the 

 weight of the skull, which was female, was reduced to 15 oz., 

 whereas the weight of a normal young skull of the same sex is about 

 28 oz. A simple absorption of the inner table would tend to increase 

 the capacity of the skull ; this does not take place, however. There 

 is diminution, proving that an actual contraction of the skull takes 

 place. This contraction of the brain case is not nearly so great as 

 that of the brain itself, the shrinkage of the brain with age must 

 therefore be accompanied by an increase in the amount of the cere- 

 bro-spinal fluid. Now, it is stated by Wakelin Barratt, in Journ. Anat. 

 Pkys., vol. xxx vii., p. 150, that in chronic atrophy of the brain of a 

 pathological nature " the atrophy of the gyri with corresponding 

 widening of the sulci and distention of the pia-arachnoid with fluid, 

 forms a striking appearance when the brain before removal is viewed, 

 in situ, from above," and he has also proved that in chronic wasting 

 diseases of the brain, such as dementia and general paralysis of the 

 insane, a very considerable enlargement of the lateral and third ven- 

 tricles takes place, this enlargement being essentially due to wasting 

 of white matter. He also remarks that the enlargement which chiefly 

 involves the lateral ventricles affects the anterior cornua and bodies 

 more than the rest of the ventricular cavity ; and that the appearance 

 of the ventricular cavity in senile atrophy (four cases) was not ob- 

 served to differ markedly in its general characters from that present 

 in general paralysis of the insane. It is probable, therefore, that the 

 normal atrophy of the brain which takes place with the advance of 

 age is accompanied both by an increase in the cerebro-spinal fluid in 

 the pia-arachnoid and by an enlargement of the cerebral ventricles. 



2. SEXUAL DIFFERENCES. 



The principal distinguishing features of a typical male skull as 

 compared with a typical female skull, such as the greater size of the 



