THE CKANIUM. 1359 



of the zygomatic bone ; a line drawn from this tubercle to the lambda gives the line 

 of the superior temporal sulcus and of the inferior cornu of the lateral ventricle. 



The zygomatic arch, an important landmark, is horizontal when the head is in 

 the natural position, and is on the same level as the inferior margin of the orbit and 

 the inion ; its superior border is at, or not infrequently a little above, the level of 

 the lower lateral margin of the hemisphere. The superior border of the zygoma may 

 be traced backwards immediately above the tragus and the external acoustic meatus 

 to become continuous with the ridge formed by the supra-mastoid portion of the 

 temporal crest. The part of the posterior root of the zygoma which lies imme- 

 diately in front of the superior end of the tragus constitutes a valuable landmark 

 which may with advantage be termed the pre-auricular point of the zygoma, while by 

 the term post-auricular point is understood that point upon the supra-mastoid crest 

 which lies immediately behind, and a finger's-breadth below, the upper attachment 

 of the auricle. The temporal vessels and the auriculo-temporal nerve cross the 

 zygoma at the pre-auricular point, and it is there that the pulsations of the temporal 

 artery may be felt during the administration of an anaesthetic, or the vessel 

 compressed for the purpose of checking bleeding from the temporal region of the 

 scalp. The termination of the auriculo-temporal nerve in the neighbourhood 

 of the parietal tuber is often the seat of a .neuralgic pain in irritative conditions 

 about the external acoustic meatus, the latter being supplied by this nerve. 



Two inches vertically above the pre-auricular point is the inferior end of the 

 central sulcus of Rolando. Two inches vertically above the middle of the zygomatic 

 arch is the pterion (spheno-parietal suture), a point which cannot be felt, but which 

 is nevertheless of topographical importance, as it overlies the lateral point (the point 

 where the lateral fissure of the brain breaks up into its three branches) and the 

 anterior branch of the middle meningeal artery. 



The frontal tuber (better marked in the child) overlies the middle frontal con- 

 volution. The parietal tuber, which varies considerably in the definiteness with 

 which it can be recognised, overlies the termination of the posterior horizontal 

 limb of the lateral fissure of the brain, and therefore also the supra-marginal convolu- 

 tion, which is named by Turner the convolution of the parietal tuler. The part of 

 the temporal crest which intervenes between the zygomatic process of the frontal 

 bone and the coronal suture lies a little above the level of the inferior frontal sulcus. 

 The highest part of the temporal crest crosses the anterior central gyrus at the 

 junction of its middle and lower thirds, that is to say, at the junction of the motor 

 areas for the arm and face. In the child the temporal muscle, which is relatively 

 much smaller than in the adult, reaches only a short distance above the squamous 

 suture, and, therefore, only as far as the level of the inferior end of the central 

 sulcus of Eolando. 



The thickness of the skull-cap varies at different parts and in different individuals. The 

 inner table is only half the thickness of the outer table, but both possess the same degree of elas- 

 ticity. When the vault is fractured from direct violence, the inner table is more extensively 

 fissured than the outer table, because the elements of the latter are compressed, while those of the 

 former are stretched apart. The weak areas at the base of the skull through which fractures are 

 liable to extend are : in the anterior cranial fossa, the orbital parts of the frontal bone, and the 

 cribriform plate of the ethmoid ; in the middle cranial fossa, the region of the glenoid cavity 

 of the temporal bone, and of the foramen ovale of the sphenoid ; in the posterior fossa, the fossae 

 of the occipital bone. The strong petrous part of the temporal is weakened by the tympanic 

 cavity and by the deep jugular fossa. 



Cranio-Cerebral Topography. Of the many methods which have been 

 devised for mapping out the relations of the cranial contents to the scalp, that 

 introduced by Professor Chiene is, probably, the most useful from a clinical 

 point of view; no figures or angles have to be remembered, and the primary 

 surface lines are drawn from bony points which are not variable, whilst the 

 secondary lines are drawn, for the most part, between mid-points of the primary 

 lines. The method is as follows (Figs. 1067 and 1068) : 



" The head being shaved, find in the median line of the skull between the . 

 glabella (G-) and the external occipital protuberance (O) the following points : 



" First, the mid-point (M) ; second, the three-quarter point (T); third, the seven- 

 eighth point (S). 



