Many of the facts mentioned above can be used as data when endeavouring to determine approximately the age of a skull at the time of death. Thus the age of young skulls can be determined with fair accuracy from the number of erupted teeth : the presence of well-formed air sinuses puts the age after puberty ; absence of fusion between basisphenoid and basioccipital places it before twenty-five ; the styloid process is not joined to the temporal until middle life ; the vomer and mesethmoid are synostosed after forty-five ; and the skull in old age is edentulous, with wasted alveolar processes, and is lighter and has thinner bones with large air sinuses.
* For further skull measurements the student must consult works on anthropology.
+ The separation of the bones over the vault no doubt enables the increase in size of the head to take place more rapidly, but probably it is not an essential factor in the increase. The greatest proportionate increase in size takes place of course during foetal life, but a more gradual growth goes on, with a marked increase in weight, from the first few years of life until adult age : as old age approaches the skull decreases somewhat in size and loses about two-fifths of its weight. The increase in size of the cranial bones, especially after they have met at the sutures, is brought about as in the other bones by addition to the surface with corresponding removal of bony tissue from their deep aspect : as growth proceeds in this way the parietal and frontal eminences become less marked.
It must be remembered that female skulls are thinner and lighter than male : they are shorter in proportion to their breadth : they are also smaller, with a capacity about one-tenth less, but this is in proportion to the smaller bulk of the female body.* The male skull is rougher and more ridged, with more prominent mastoid processes, zygomatic arches, and occipital protuberance : the superciliary ridges are more rounded and prominent, but the parietal eminences are less marked than in the female skull.. In other words, the female skull preserves somewhat an appearance of immaturity. The tympanic plate is said to be more developed in the male and shows a sharp border, while in the other sex the edge is more rounded. The female palate is narrower than the male. There is little sexual difference before puberty.
In comparison of skulls of different races it is always advisable, when possible, to compare the measurements of male skulls. For such measurements and indices the student must consult works dealing with anthropometry, but a few may be given here as they are in common use :-
(a) Maximum length-male, about 8 inches or less ; female, about 1/2 inch less.
(b) Maximum circumference (varies between 17 1/2 inches and 21 1/2 inches). In Europeans -male, about 20 1/2 inches ; female, about 19J inches.
(c) Cephalic index :
Cephind of Europeans is 75 to 80 (mesaticephalic). ,, some races is over 80 (brachycephalic) others is under 75 (dolichocephalic). Usually rather larger in women than in men, owing to relatively greater breadth. (All these measurements must of course be made between the same points if they are to have any value in comparing different skulls, and these points are not always similar in the measurements given by individual observers).
(d) The Facial Angle.-This estimates the amount of prognathism or projection of the face bones. It is obtained in various ways, depending in general cn a basal skull line contrasted with a line drawn from the nasion to a projecting point on the upper jaw. The contained angle is the one required. In older measurements the opposite angle was taken, so that the angle increased as prognathism decreased.
It may not be out of place to point out here that the anthropoid skull is most like the human type in its young state, diverging from it as it develops. The skull of a chimpanzee is distinguished from that of man by the sloping plane of its foramen magnum already mentioned, the smallness of its condyles, the diastema in the canine region of its jaws, its large intermaxillary bone, jaws, teeth, and petrous bone, the want of a crista galli and flatness of its (usually fused) nasals, and the presence of a well-marked post-glenoid process. In this last character the negro skull resembles it to some extent.