CRANIO-CEREBRAL TOPOGRAPHY. 5 



angle of the parietal bone, is from 15 to 20 mm. (in extreme cases even 25 mm.) 

 above, and somewhat external to the mid-point of, this line. The distance of the 

 descending part of the sinus from the posterior wall of the auditory canal is usually 

 from 10 to 12 mm., but may be as little as 2 mm. The course of this part of the 

 sinus corresponds roughly to the line of reflection of the skin from the pinna to the 

 head posteriorly (Birmingham). The depth of the sinus from the surface of the 

 mastoid varies from 1 to 15 mm., with an average of 7 mm. ; and its breadth 

 ranges from 5 to 15 mm. The sinus is often much wider in its mastoid than in its 

 occipital segment. The right sinus is generally larger, projects more forwards, and 

 approaches nearer to the surface than the left. The lateral sinus may be exposed 

 by an opening in the bone immediately below the anterior part of the parieto 

 mastoid suture, or having its centre 25 mm. (1 inch) behind the highest point of 

 the orifice of the osseous external auditory meatus. 



The anterior and larger division of the middle meningeal artery runs upwards 

 and backwards within the skull in the fore part of the temporal region, and would 

 be reached at points equal distances, one inch, one inch and a half, and in most 

 cases two inches, above the zygoma and behind the external angular process of the 

 frontal bone. It will be remembered that the vessel in this part of its course is 

 lodged in a deep groove, sometimes a canal, on the antero-inferior angle of the 

 parietal bone. The ramifications of the posterior division of the artery are variable 

 in number and position. 



Craiiio-cerebral topography. Extent of the cerebral hemisphere. The upper 

 margin of the cerebral hemisphere extends from the lower part of the glabella nearly 

 to the external occipital protuberance. It does not quite reach the middle line, 

 being separated from its fellow by an interval which corresponds to the superior 

 longitudinal sinus, and like that increases in breadth posteriorly, where it measures 

 fully 1 cm. Owing to the lateral deviation of the sinus, the margin of the hemi- 

 sphere commonly approaches nearer to the middle line on the left side than on the 

 right. Beiow the sinus the mesial surfaces of the two hemispheres are nearly in 

 contact, being separated only by the thickness of the falx cerebri. Inferiorly, the 

 cerebral hemisphere reaches in front nearly to the eyebrow, at the side to the upper 

 margin of the zygoma, and behind to the superior curved line of the occipital bone. 

 The lower limit of the hemisphere is more precisely indicated by marking out its 

 lateral margin, which consists of two parts frontal and occipito-temporal. The 

 frontal part begins internally close above the naso-frontal suture (which is felt at 

 the bottom of the depression below the glabella), rises in an arch as it passes out- 

 wards, being about 8 mm. above the centre of the supraorbital border of the frontal 

 bone, and crosses the temporal crest just below the deepest point of the hollow 

 formed by the frontal bone immediately above the external angular process. From 

 the temporal crest the frontal margin descends slightly in the fore part of the 

 temporal fossa to a spot about 25 mm. behind the external angular process, where 

 it meets the foremost part of the temporal margin in a receding angle, which 

 corresponds to the stem of the fissure of Sylvius. The occipito-temporal division of 

 the lateral margin begins posteriorly at the occipital pole of the hemisphere, which 

 is placed a little (5 to 15 mm.) above and outside the external occipital protuber- 

 ance, and then follows the arch of the lateral sinus, as described above, to the back 

 of the ear. Crossing here the supramastoid crest, the margin is continued 

 forwards about 6 mm. (varying from 3 to 9 mm.) above the roof of the external 

 auditory meatus, and then on a level with the upper border of the zygomatic arch 

 for about the posterior half of its length. Then curving gradually upwards, the 

 border reaches its foremost point, corresponding to the temporal pole of the hemi- 

 sphere, about 20 mm. above the zygoma and 15 mm. behind the external angular 



