62 PRACTICAL ANATOMY. 



which is such as to effectually resist violence to the organ 

 which it contains. The cranium is about seven inches 

 long, five inches at its widest part, and five inches high 

 from the vertex to the base. Its circumference is about 

 nineteen inches. Its walls average three-sixteenths inch 

 in thickness. If divided in the median line, it is found 

 not to be absolutely symmetrical. Marked asymmetry 

 of the cranium is frequently observed in the insane, and 

 also in the criminal classes. The skull presents for 

 examination five regions, a superior, an inferior, two 

 lateral, and an anterior. The superior region is known 

 as the vertex, or summit. It is bounded in front by the 

 superciliary ridges and the glabella ; behind, by the 

 superior curved lines of the occipital ; laterally, by a 

 line drawn from the superior curved line of the occipital 

 to the temporal ridge, and thence to the external angular 

 process of the frontal. The vertex is formed by the 

 frontal, the two parietal, and the occipital bones. From 

 before backward are seen, on each side of the median 

 line : the frontal eminence, the remains of the frontal 

 suture, the parietal eminence or boss, the parietal fora- 

 men, and, in some skulls, at the angle of articulation 

 between the two parietal and the apex of the occipital, 

 a separate piece of bone, sometimes a number, consti- 

 tuting islands of bone held firmly in position by dentated 

 processes. They are called Wormian bones. They are 

 also found, but less frequently, at the junction of the 

 coronal and sagittal sutures. In some of the lower ani- 

 mals, as the sheep, they are the rule. The development 

 of Wormian bones in these positions is due to the deposit 

 of separate ossific centres. In the foetus the bones of 

 the cranium are not fully developed, hence not solidly 

 articulated, and, by slight pressure, their edges, particu- 

 larly those forming the vertex, can be made to overlap. 



