186 PROCEEDINGS OF THE ANATOMICAL AND ANTHROPOLOGICAL 



Now, in the heads of the subjects measured in the post-mortem 

 room at the Middlesex Hospital we found that there was in both 

 senses a gradual diminution in the size of the head, accompanying 

 advance in age and commencing at about twenty-five. The amount 

 of this decrease for each of the principal diameters of the head is 

 shown in Fig. 2, p. 138, Biometrikn, vol. iv. ; in which it is shown that 

 the shrinkage is greater in the female than in the male subject, and 

 affects chiefly the auricular height. 



Part of this diminution in the size of the head is due to a 

 thinning of the scalp, dependent on atrophic changes in the skin and 

 subcutaneous tissue, and more especially atrophy of the hair follicles 

 (see Biometrlka, vol. iv., p. 111). 



The lessening of the diameters of the skull due to atrophy of the 

 scalp is shown by the following figures : 



Reduction of Diameter 

 Diameter of Head. caused by 



Atrophy of the Scalp. 



Longitudinal - O81 mm. 



Transverse - 0'88 mm. 



Vertical - 0'29 mm. 



This is clearly not sufficient to account for the whole of the decrease 

 in the size of the head, and more especially is this the case with the 

 vertical diameter. 



I have therefore made a comparison of the size of aged skulls 

 with that of young adult skulls, taking a series of skulls in which the 

 age was recorded to be above fifty, or in which the sutures were closed, 

 the teeth much worn or fallen out, and the alveolar processes ab- 

 sorbed, and comparing these with skulls of young adults, mostly 

 between twenty-five and forty years of age, and of corresponding 

 nationality and sex (Tables VII.-X.). 



Now, it is important to note that the diminution in the si/e of 

 the skull, which occurs with the advance in age, affects not only the 

 external measurements, but also the capacity, as the reduction of the 

 former might be produced by absorption of the outer table of the 

 skull, due to the atrophy of old age. This atrophy is sometimes met 



