2i8 THE HEAD AND NECK 



THE HEAD. 



Bony Landmarks. The External Occipital Protuberance 

 lies just above a small depression, which indicates the upper end 

 of the nuchal furrow when the head is held erect. Two inches 

 above it in the median line the Lambdoidal Suture can be recog- 

 nised as an irregular depression. The Parietal Tuber (Eminence), 

 which overlies the supra-marginal convolution of the brain,, 

 can be felt on the side of the skull about two inches above the 

 auricle. It is crossed by the Superior Temporal Line (Crest), 

 which can be traced downwards and forwards to the zygomatic 

 (external angular) process of the frontal bone, and downwards 

 and backwards to a point a little above and behind the mastoid 

 process. The Asterion, which corresponds to the articulation 

 of the mastoid (postero-inferior) angle of the parietal bone with 

 the temporal, forms a depression above and behind the external 

 acoustic meatus. It lies about midway between the Sylvian 

 point (p. 229) and the external occipital protuberance. Other 

 bony landmarks have been dealt with on pp. 170, 171. 



The Skin of the Scalp contains a large number of sebaceous 

 glands, and is therefore a common site for sebaceous cysts or 

 wens. These swellings are embedded in the superficial fascia, 

 which in this region consists of a dense network of fibrous tissue 

 containing very small lobules of fat. They can be moved with 

 the scalp, and this feature distinguishes them from tumours in 

 connection with the pericranium. 



Numerous arteries supply the scalp, ramifying for the most 

 part in the subcutaneous layer. They are derived from both 

 the external and the internal carotid arteries, and ascend to- 

 wards the vertex from the orbit, face, and neck. A free anasto- 

 mosis occurs between the two groups of vessels and across the 

 median line. In consequence, ligature of one external carotid 

 fails to cure a cirsoid aneurism of the superficial temporal artery. 

 Subcutaneous haemorrhage is limited in amount owing to the 

 density of the tissue, and for the same reason superficial septic 

 infections remain localised and are extremely painful. When 

 one of these vessels is cut the bleeding is plentiful, as its wall 

 is held open and prevented from retracting by its attachment 

 to the fibrous septa. At the same time the density of the sub- 

 cutaneous tissue renders the cut vessels difficult to catch, but 

 moderate pressure usually suffices to stop the haemorrhage. 



