904 



THE NERVOUS SYSTEM 



by the orbital surface of the frontal lobe, rests upon the upper surfaces of the orbital plate of 

 the frontal bone and the lesser wing of the sphenoid. It is, therefore, in close relation with the 

 upper wall of the orbital cavity. The posterior part, behind the stem of the lateral fissure, 

 begins with the anterior portion of the temporal lobe, including its pole. The pole itself 

 projects against the orbital plate of the great wing of the sphenoid bone, and it is in relationship 

 with the posterior part of the lateral wall of the orbit. The basal surface of the hemisphere, 

 behind the pole of the temporal lobe is in contact with the upper surfaces of the great wing of 

 the sphenoid and the petrous part of the temporal bone. 



The convex surfaces of the cerebral hemispheres have the most extensive relationships with 

 the cranial wall, and it is more especially to these surfaces that the surgeon turns his attention. 

 The general area in which the convex surface of each cerebral hemisphere is in relation with the 

 skull bones is readily indicated by a series of lines which correspond with the positions of its 

 superciliary, infero-lateral, and supero-mesial borders. 



The Une marking the supercihary margin of the hemisphere commences at the nasion (the 

 mid-point of the fronto-nasal suture) ; it passes lateralward above the superciliary ridge, crosses 

 the temporal ridge, then, turning posteriorly in the temporal fossa, it reaches the parieto- 

 sphenoidal suture, and continues backward along it to its posterior extremity. 



Fig. 712. — Drawing of a Cast op the Head of a Newly Born Male Infant. 

 (Prepared by Professor Cunningham to illustrate cranio-cerebral topography.) 



Interparietal 

 sulcus 

 External part of 

 parieto-occip- 

 ital fissure 



Central sulcus 

 (Rolandi) 



Position of pari- 

 etal eminence 

 Position of 

 frontal eminence 

 Lateral fissure 



Superior tem- 

 poral sulcus 



The line marking out the infero-lateral border commences at the posterior end of the parieto- 

 sphenoidal suture, whence it passes downward, in front of the spheno-squamous suture, to the 

 infra-temporal crest (pterygoid ridge) ; there it turns posteriorly and, running parallel with and 

 mesial to the zygomatic arch, it crosses the root of the zygoma, and, ascending slightly, it passes 

 above the external auditory meatus. Continuing backward with an inclination upward it 

 reaches a point immediately above the asterion; thence it descends, and, crossing the inferior 

 part of the lambdoid suture and the superior nuchal line, it passes medialward to the inferior 

 part of the external occipital protuberance. 



The supero-mesial border of the hemisphere is defined by a line which runs from the nasion 

 to the inion. This line should be drawn about 6 mm. lateral to the sagittal suture, because 

 the mesial area is occupied by the superior sagittal sinus, and it should be further away from 

 the middle Une on the right than on the left side, because the sinus tends to lie more to the 

 right side. 



The area of i]vi skull wall enclosed by the throe lines which mark the positions of the super- 

 cihary, infero-lateral, and the supero-mesial borders of the cerebral hemisphere is formed by the 

 vertical plate of the frontal l)one, the parietal bone, the great wing of the sphenoid, the squamous 

 part of the temporal, and the upper section of the supra-occipital segment of the occipital bone. 

 It covers the outer surfaces of t lie frontal, parietal, temporal, and occipital lobes of the cerebrum 

 and the fissures and sulci whicli bound and mark thorn. 



In every consideration of the topogniphioal relations of the cerebral gyri to the walls of the 

 cranial cavity it must bo borne in mind that the conditions are not constant, and that, therefore, 

 the relations are variable. The tliroo main factors upon which this variability depends are age, 

 sex, and the shape of the skull. As examples of the variations which occur it may be mentioned 

 that the lateral cerebral fissure is rolativoly higher in the child than in the adult (compare 

 figs. 711 anfl 712). The supero-mesial end of the central sulcus is further away from the coronal 

 suture in the female and in the child than in the adult male, and in dolichocephalic than in 



