CRANIO-CEREBRAL TOPOGRAPHY 



1339 



travel along the upper border of this process about 6 mm. {\ in.) above the roof 

 of the external auditory meatus (fig. 1089), and thence just above the base of 

 the mastoid and the posterior inferior angle of the parietal, and so along the 

 hnea nuchse suprema, and corresponding to the tentorium and horizontal part 

 of the transverse (lateral) sinus, to the external occipital protuberance. 



The upper margin of each hemisphere would be represented by a line drawn 

 from just below the glabella, sufficiently to one side of the middle line to allow for 

 the falx and superior sagittal sinus, to one immediately above the superior external 

 occipital protuberance and inion. 



B. Relation of the chief fissures and convolutions to the skull. C. Local- 

 isation of the chief sulci and gyri. These headings will be taken together. 



It will be well first to incUcate the position of the chief sutures which mark off 

 the parietal bone, under which lies that part of the brain which is most important 

 to the surgeon — the motor area. The upper limit of the bone will be indicated by 

 the line already spoken of as giving the upper margin of the hemisphere — the 

 sagittal line, or Sagittal suture. The anterior limit of the parietal bone, formed 



Fig. 



1089. — The Outline of the Brain and its Fissures in Relation to the Sutures 

 OF the Skull. (Cunningham.) 

 s.M. Supraciliary margin of the cerebrum, i.l.m. Infero-lateral margin of the cerebrum. 

 l.s. Position of highest part of the arch of the transverse sinus, r. Central sulcus (Fissure of 

 Rolando), s^. Anterior horizontal limb of lateral fissure, s^. Anterior ascending limb of 

 lateral fissure, s^. Posterior horizontal limb of lateral fissure, p.b. Opercular portion of the 

 inferior frontal convolution, p.t. Triangular portion of the inferior frontal convolution. 

 P.O. Oi'bital portion of the inferior frontal convolution. 



by the coronal suture, may be traced thus : The point where it leaves the sagittal 

 suture (the bregma) will be found by drawing a line from a point just in front of 

 the external auditory meatus (the pre-auricular point) (fig. 1085) straight upward 

 on to the vertex; from this point a line drawn downward and forward to the 

 middle of the zygomatic arch would indicate that of the coronal suture. Under 

 this suture lie the posterior extremities of the three frontal convolutions; for the 

 frontal lobe lies not only under the frontal bone, but extends backward under the 

 anterior part of the parietal, the central sulcus (fissure of Rolando) , which separates 

 the frontal from the parietal lobe, lying from 3.7 to 5 cm. (1| to 2 in.) behind the 

 coronal suture at its upper extremity and about 2.5 cm. (1 in.) at its lower. 



The squamoso -parietal suture, which marks the lower border of the anterior two-thirds 

 of the parietal bone, is not so easy to define, owing to the irregularity and variations of its curve. 

 Its highest point is usually 4. .3 cm. (If in.) above the zygoma. 



The lambdoid suture, which forms the posterior boundary of the parietal bone, will be 

 marked out by a line which starts from a point (lambda) about 6.2 cm. (2| in.) above the 

 external occipital protuberance, and runs downward and forward to a point on a level with 

 the zygoma, .3.7 cm. (1^ in.) behind and 1.2 cm. (^ in.) above the centre of the meatus. 



