230 THE HEAD AND NECK 



The Posterior Ramus of the lateral fissure of Sylvius runs backwards, 

 forming the upper boundary of the temporal lobe ; and, posteriorly, it turns 

 upwards into the parietal lobe. It may be mapped out on the surface by 

 drawing a line from the Sylvian point backwards for three inches in the 

 direction of the lambdoidal suture and then upwards for one inch. At its 

 termination the ramus lies under cover of the parietal tuber (eminence), and 

 is surrounded by the supra-marginal convolution. The word-hearing centre 

 is placed in the superior temporal gyms, below the middle part of the pos- 

 terior ramus. Immediately behind the supra-marginal convolution lies the 

 angular gyrus, which contains the word-seeing centre. It can be exposed by 

 trephining the skull a little below and behind the parietal tuber. 



The occipital lobe is covered by the upper part of the squamous portion 

 of the occipital bone. It contains the higher visual centres, but they are 

 situated chiefly on its medial surface. 



The Middle Meningeal Artery (p. 181) enters the skull 

 through the foramen spinosum, and runs laterally and slightly 

 forwards over the floor of the middle cranial fossa between the 

 dura mater and the bone. One finger's breadth above the mid- 

 point of the zygomatic arch, it divides into anterior and posterior 

 branches. The former runs upwards and crosses the deep sur- 

 face of the pterion opposite the Sylvian point, and is then con- 

 tinued upwards along the anterior border of the motor area. 

 The posterior branch runs backwards parallel to the posterior 

 ramus of the lateral fissure of Sylvius and about three-quarters 

 of an inch above the level of the zygomatic arch. 



Surgical Approach to the Middle Cranial Fossa. 

 The middle cranial fossa is opened in operations in connection 

 with the semilunar (Gasserian) ganglion, in ligature of the 

 branches or main trunk of the middle meningeal artery, and in 

 subtemporal decompression. The approach is very much the 

 same in each case. The incision divides the skin and superficial 

 fascia from the zygomatic (external angular) process of the 

 frontal bone along the superior temporal line, and descends 

 posteriorly to a point in front, above, or behind the auricle, as 

 the case may be. In this way the upper branches of the facial 

 nerve, which lie parallel to and a little below the base of the 

 flap, are preserved intact. The flap thus mapped out is turned 

 downwards till the zygomatic arch is reached. The skull may 

 be exposed by turning down a flap, consisting of the temporal 

 fascia and muscle, or the fascia alone may be dissected down- 

 wards and the muscle may be split and each half retracted 

 (Cushing's intermusculo-temporal method in ligature of the 

 anterior division of the middle meningeal artery). 



The point of application of the trephine varies with the 

 individual operation. After a circular disc of bone has been 



