chap, ii.) BONY VAULT OF THE CRANIUM. 19 



separated is the os epuctal of the French (Fig. 4 A), 

 the interparietal bone of some animals. 



Parietal fissures. In the developing parietal 

 bone, fibres concerned in ossification radiate towards the 

 periphery from t\vo nuclei about the centre of the bone. 

 An interfibrillar space, larger than the rest, is seen about 

 the fifth month to separate the loose osseous fibres which 

 abut on the posterior part of the sagittal border from the 

 stronger fibres which form the rest of this border (Pozzi). 

 This is the parietal fissure. It usually closes and leaves 

 no trace, but it may persist in part as a suture-like 

 fissure, and be mistaken for a fracture (Fig. 4 B). If 

 the fissure persists equally on the two sides an elong- 

 ated lozenge-shaped gap is left, the sagittal fontanelle. 

 It is situate about an inch in front of the lambda (Fig. 

 4 c). The parietal foramina are remains of this interval. 



Wormian bones. These irregular bones may 

 be mistaken for fragments produced by fracture. 

 They are most usually met with in the lambdoid 

 suture. One Wormian bone deserves especial notice, 

 as it may be met with in trephining over the middle 

 meningeal artery. It exists between the anterior 

 inferior angle of the parietal bone and the great wing 

 of the sphenoid. It is scale-like, and gives the im- 

 pression that the tip of the great wing had been 

 separated. It is known as the epipteric bone. 



Necrosis is fairly common on the vault of the 

 skull, and most often attacks the frontal and parietal 

 bones, while, for reasons that are not very obvious, it 

 is rare in the occipital bone. The external table is 

 frequently necrosed alone, it being more exposed to 

 injury and less amply supplied with blood than is the 

 internal table. From the converse of these reasons 

 it happens that necrosis of the internal table alone is 

 but rarely met with. Necrosis involving the entire 

 thickness of the bone may prove very extensive, and 

 in a case reported by Saviard, practically the whole of 



