GO 



THE SKELETON. 



Surfaces. The external surface (Fig. 26) is convex, smooth, and marked about 

 its centre by an eminence called the parietal eminence, which indicates the point 

 where ossification commenced. Crossing the middle of the bone in an arched 

 direction are two well-marked curved lines or ridges, the upper and lower temporal 

 ridges ; the former gives attachment to the temporal fascia, while the latter indicates 

 the upper limit of the origin of the temporal muscle. Above these ridges the 

 surface of the bone is rough and porous, and covered by the aponeurosis of the 

 Occipito-frontalis ; between them the bone is smoother and more polished than 

 the rest ; below them the bone forms part of the temporal fossa, and affords attach- 

 ment to the temporal muscle. At the back part of the superior border, close to 

 the sagittal suture, is a small foramen, the parietal foramen, which transmits a 

 vein to the superior longitudinal sinus, and sometimes a small branch of the 

 occipital artery. Its existence is not constant, and its size varies considerably. 



The internal surface (Fig. 27), concave, presents depressions for lodging the 

 convolutions of the cerebrum and numerous furrows for the ramifications of 

 the middle meningeal artery ; the latter runs upward and backward from the 



Posterior 



superior 



angle. 



Posterior 



inferior 



angle. 



^.Anterior 

 superior 

 angle. 



FIG. 27. Left parietal bone. Internal surface. 



anterior inferior angle and from the central and posterior part of the lower border 

 of the bone. Along the upper margin is part of a shallow groove, w r hich, when 

 joined to the opposite parietal, forms a channel for the superior longitudinal 

 sinus, the elevated edges of which afford attachment to the falx cerebri. Near 

 the groove are seen several depressions, especially in the skulls of old persons ; 

 they lodge the Pacchionian bodies. The internal opening of the parietal foramen 

 is also seen when that aperture exists. 



Borders. The superior, the longest and thickest, is dentated to articulate with 

 its fellow of the opposite side, forming the sagittal suture. The inferior is divided 

 into three parts : of these, the anterior is thin and pointed, bevelled at the expense 

 of the outer surface, and overlapped by the tip of the great wing of the sphenoid ; 

 the middle portion is arched, bevelled at the expense of the outer surface, and 



