CRANIO-CEREBRAL TOPOGRAPHY 



1341 



The posterior limb of the lateral fissure also may be represented by a line bisecting the angle 

 RiSH and ending behind at the point S^ where it cuts the vertical MRi. 



Some further points in the surgical anatomy of the cranium must be referred to: — The mid- 

 dle meningeal artery. This vessel, entering the middle fossa by the foramen spinosum, grooves 

 the great wing of the sphenoid and divides into two branches. The anterior grooves the 

 anterior inferior angle of the parietal bone, and is then continued upward and slightly back- 

 ward between the coronal suture and central sulcus (fig. 1090), almost to the vertex; the posterior 

 branch takes a lower level, running backward under the squamous bone to supply the parietal 

 and anterior part of the occipital bones. If a skull, bisected antero-posteriorly, be held up to 

 the light, it will be seen how thin are the bones over the chief branches of this vessel, thus 

 accounting for the slight violence sometimes sufficient to rupture it. The groove it occupies 

 in the parietal is sometimes converted into a canal. A wounded artery retracting here may be 

 very difficult to secure. The veins which accompany the artery and which lie lateral to it 



Fig. 1091. — Cerebral Topography and Localization. (Gushing, from Keen's Surgery.) 



in the groove are thin-walled and sinus-like before they open into the spheno-parietal sinus, 

 another explanation of the obstinacy of this haemorrhage. According to the point of ruptm-e, 

 three haematomata should be remembered (Kronlein), anterior or fronto-temporal; middle, 

 or temporo-parietal; and posterior, or parieto-occipital. The first two are much the most 

 frequent, and exposure of the pterion, with free removal of the adjacent bone, will suflice for 

 dealing with them. 



Drainage of the lateral ventricle. — (1) Where the anterior fontanelle is closed, Poirier and 

 Keen have opened the inferior cornu through the middle temporal convolution, the pin of 

 the trephine being placed 3.1 cm. {l\ in.) behind the external auditory meatus, and about the 

 same distance above Reid's base-line which is drawn from the lower margin of the orbit through 

 the mid-point of the external auditory meatus. The needle should here be directed to a point 



