Head and Neck. 399 



to this sutural membrane on its under surface, there is, 

 therefore, by means of this membrane a certain 

 amount of continuity between the pericranium above 

 and the dura mater below. The pericranium differs from 

 the periosteum that covers the bones elsewhere, in that 

 its osteo-genetic layer is almost wanting; hence, When 

 the pericranium is separated from the bone beneath in in- 

 juries, etc., necrosis does not result to the same degree as 

 it does when the periosteum is stripped off a bone, since, 

 in the latter case, the main supply of blood is cut off, 

 whereas, in the former, i.e., in the case of the skull, the 

 main supply of blood is brought by the meningeal vessels 

 bf the dura mater and not by the pericranium 

 < nor does any involucre or deposit of bone 

 take place, when the pericranium is inflamed, as it 

 does when the periosteum is affected, because of the al- 

 most entire absence of the osteo-genetic or bone forming 

 layer. 



Nerves and Bloodvessels of the Scalp. These struc- 

 tures are contained in the superficial fascia and hence 

 union can occur in very extensive wounds of the scalp in 

 which large portions have been raised from the bones be- 

 neath, since these portions, themselves, contain the blood- 

 vessels necessary for their nourishment. 



Landmarks for the Nervesof the Scalp. In front, 

 over the glabella, is the supratrochlear nerve; next run- 

 ning upwards from the junction of the inner and middle 

 thirds of the supra-orbital margin is the supra-orbital 

 nerve; in the temporal region, near the outer canthus of 

 the eye, and about one inch above the zygoma is the tem- 

 poral branch of the orbital from the superior maxillary ; 

 over the temporal fossa are the temporal branches of the 

 facial nerve and the superficial temporal branches of the 

 auriculo -temp oral. Over the posterior portion of the pin- 



