CRANIOLOGY 



197 



of puberty, when a second period of activity occurs : this results in an increase in all directions, 

 but it is especially marked in the frontal and facial regions, where it is associated with the develop- 

 ment of the air sinuses. 



Obliteration of the sutures of the vault of the skull takes place as age advances. This process 

 may commence between the ages of thirty and forty, and is first seen on the inner surface, and 

 some ten years later on the outer surface of the skull. The dates given are, however, only approxi- 

 mate, as it is impossible to state with anything like accuracy the time at which the sutures are 

 closed. Obliteration usually occurs first in the posterior part of the sagittal suture, next in the 

 coron. 1, and then in the lambdoidal. 



In old age the skull generally becomes thinner and lighter, but in a small proportion of cases 

 it increases in thickness and weight, owing to an hypertrophy of the inner table. The most strik- 

 ing feature of the old skull is the diminution in the size of the maxillae and mandible consequent 

 on the loss of the teeth and the absorption of the alveolar processes. This is associated with a 

 marked reduction in the vertical measurement of the face and with an alteration in the angles 

 of the mandible. 



Frontal fontanel 





Mastoid fontanel 



Sphenoidal fontanel 

 FIG. 198. Skull at birth, showing sphenoidal and mastoid fonticuli. 



SEXUAL DIFFERENCES IN THE SKULL. 



Until the age of puberty there is little difference between the skull of the female and that of 

 the male. The skull of an adult female is, as a rule, lighter and smaller, and its cranial capacity 

 about 10 per cent, less, than that of the male. Its walls are thinner and its muscular ridges less 

 strongly marked; the glabella, superciliary arches, and mastoid processes are less prominent, 

 ard the corresponding air sinuses are small or rudimentary. The upper margin of the orbit is 

 sharp, the forehead vertical, the frontal and parietal eminences prominent, and the vault some- 

 w iat flattened. The contour of the face is more rounded, the facial bones are smoother, and the 

 maxillae and mandible and their contained teeth smaller. From what has been said it will be seen 

 that more of the infantile characteristics are retained in the skull of the adult female than in that 

 of the adult male. A well-marked male or female skull can easily be recognized as such, but in 

 some cases the respective characteristics are so indistinct that the determination of the sex may 

 be difficult or impossible. 



CRANIOLOGY. 



Skulls vary in size and shape, and the term craniology is applied to the study of these varia- 

 tions. The capacity of the cranial cavity constitutes a good index of the size of the brain which 

 it contained, and is most conveniently arrived at by filling the cavity with shot and measuring 

 the contents in a graduated vessel. Skulls may be classified according to their capacities as 

 follows: 



1. Microcephalic, with a capacity of less than 1350 c.cm. e. g., those of native Australians 

 ard Andaman Islanders. 



2. Mesocephalic, with a capacity of from 1350 c.cm. to 1450 c.cm. e. g., those of African 

 negroes and Chinese. 



3 Megacephalic, with a capacity of over 1450 c.cm. e. g., those of Europeans, Japanese, and 

 kimos. 





