1292 



SURFACE ANATOMY AND SURFACE MARKINGS 



side by the upper two-thirds of a line from the lambda to the tip of the mastoid 

 process. The sagittal suture is in the line joining the lambda to the bregma. The 

 position of the coronal suture on either side is sufficiently represented by a line 

 joining the bregma to the center of the zygomatic arch. 



The floor of the middle fossa of the skull is at the level of the posterior three- 

 fourths of the upper border of the zygomatic arch; the articular eminence of the 

 temporal bone is opposite the foramen spinosum and the semilunar ganglion. 



FIG. 1197. Drawing of a cast by Cunningham to illustrate the relations of the brain to the skull. 



Brain (Figs. 1197, 1198). The general outline of the cerebral hemisphere, on 

 either side, may be mapped out on the surface in the following manner. Starting 

 from the nasion, a line drawn along the middle of the scalp to the inion represents 

 the superior border. The line of the lower margin behind is that of the transverse 

 sinus (see page 1294), or more roughly a line convex upward from the inion to the 

 posterior root of the zygomatic process of the temporal bone; thence along the 

 posterior two-thirds of the upper border of the zygomatic arch where the line turns 

 up to the pterion; the front part of the lower margin extends from the pterion to 

 the glabella about 1 cm. above the supraorbital margin. The cerebellum is so deeply 

 situated that there is no reliable surface marking for it; a point 4 cm. behind and 

 1 .5 cm. below the level of the auricular point is situated directly over it. 



The relations of the principal fissures and gyri of the cerebral hemispheres to 

 the surface of the scalp are of considerable practical importance, and several 

 methods of indicating them have been devised. Necessarily these methods can 



