Chap. T.] THE SCALP. 5 



long and severe pressure. The scalp, by its vascu- 

 larity, is saved to a great extent from this evil, and is 

 much less liable to slough than are the soft pai-ts 

 covering such bones as the condyles of the humerus or 

 the sacrum. But such an effect is sometimes pro- 

 duced, as in a case I saw, where the tissues over the 

 frontal and occipital regions sloughed from the con- 

 tinued application of a tight bandage put on to arrest 

 bleeding from a frontal wound. 



The pericranium is but slightly adherent to 

 the bone, except at the sutures, where it is intimately 

 united. In lacerated wounds this membrane can be 

 readily stripped from the skull, and often, in these 

 injuries, extensive tracts of bone are laid bare. The 

 pericranium differs somewhat in its functions from the 

 periosteum that covers other bones. If the periosteum 

 be removed to any extent from a bone, the part from 

 whence it is removed will very probably perish, and 

 necrosis from deficient blood supply result. But the 

 pericranium may be stripped off a considerable part of 

 the skull vault without any necrosis, save perhaps a 

 little superficial exfoliation, following in consequence. 

 This is explained by the fact that the cranial bones 

 derive their blood supply mainly from the dura mater, 

 and are therefore to a considerable extent independent 

 of the pericranium. A like independence cannot be 

 claimed for the periosteum covering other bones, since 

 that membrane brings to the part it covers a very 

 copious and essential contribution to its blood supply. 

 This disposition of the pericranium is also well illus- 

 trated by its action in cases of necrosis of the cranial 

 bones. In necrosis of a long bone, the separation of 

 the sequestrum is attended with a vigorous periostea! 

 growth of new bone, which repairs the gap left after 

 the removal of such sequestra. In necrosis of the 

 vault of the skull, however, no new bone is, as a 

 rule, formed, and the gap remains unrepaired. The 



