io SURGICAL APPLIED ANATOMY. [Chap. i. 



haemorrhage be determined as follows : A line is 

 drawn around the skull at the level of the upper margin 

 of the orbit, and is throughout parallel with Reid's 

 base-line, Fig. 2. (See also page 35.) The trephine 

 is first placed at a point on this line, which is from \\ 

 to 1^- inches (according to age and size of head) 

 behind the external angular process of the frontal 

 bone (A, Fig. 2). Should no clot be revealed, a second 

 hole is made upon the same line just below the 

 parietal eminence, and at a point where a vertical line 

 carried up from the posterior border of the mastoid 

 process bisects the line already given (B, Fig. 2). 



Trephining for intracranial abscess. The abscess 

 is often due to middle-ear disease, and is then very 

 commonly found in the temporo-sphenoidal lobe or in 

 the cerebellum. It is estimated to be three times 

 more common in the cerebrum than in the cerebellum. 



The abscess of the temporo-sphenoidal lobe is 

 usually found, according to Mr. Bai'ker, between two 

 lines drawn at right angles to Reid's base-line. These 

 lines are about 1^ inches apart ; one passes through 

 the meatus, the other about 1^ inches behind that 

 opening (xx, Fig. 2). The trephine should be intro- 

 duced in the centre of the space marked out by these 

 two lines, and at a distance of about li inches above 

 the base-line (c, Fig. 2). 



In dealing with an abscess of the cerebellum, the 

 best spot to select is, in the adult, 1 inches behind 

 the centre of the meatus and 1 inch below the base- 

 line (E, Fig. 2). 



Trephining for cerebral tumour. The position 

 of the opening in the skull is obviously determined 

 by the localising symptoms. It is remarkable that 

 little trouble from haemorrhage has attended these 

 operations. 



In any case, after trephining, the portion or 

 portions ot' bone removed may if properly treated 



