chap, i.j THE SCALP. 9 



fascia ; (5) the temporal muscle ; (6) the deep temporal 

 vessels ; and (7) the pericranium. In trephining the 

 skull generally, the comparative thickness of the 

 cranial wall in various parts should be borne in mind 

 (page 24), and the large arteries of the scalp should 

 be avoided if possible. The trephine should not be 

 applied over the frontal sinuses, which are often of 

 large size in the aged, and should, when possible, keep 

 clear of the sutures, owing to the frequent exit of 

 emissary veins at or about suture lines. Especially 

 must the superior longitudinal sinus be avoided, which 

 runs backwards in the middle line, and the lateral 

 sinus, whose course is represented by a line drawn 

 horizontally from the occipital protuberance to a 

 point about one inch behind the external nieatus of 

 the ear, where it turns downwards to groove the mas- 

 toid process. 



The zygoma may be broken by direct or in- 

 direct violence. In the latter case the violence is such 

 as tends to thrust the upper jaw or malar bone back- 

 wards. When due to direct violence, a fragment may 

 be driven into the temporal muscle, and much pain 

 caused in moving the jaw. In ordinary cases there is 

 little or no displacement, since to both fragments the 

 temporal fascia is attached above and the masseter 

 below. 



The vessels and nerves of the scalp. The 

 supraorbital artery and nerve pass vertically upwards 

 from the supraorbital notch, which is situate at the 

 junction of the middle with the inner third of the 

 upper orbital margin. Nearer the middle line the 

 frontal artery and supratrochlear nerve ascend. This 

 artery gives life to the flap that in rhinoplasty is 

 taken from the forehead to form a new nose. The tem- 

 poral artery, with the auriculo-temporal nerve behind 

 it, crosses the base of the zygoma just in front of 

 the ear. The branches of this artery, especially the 



