THE PARIETAL BONES 37 



artery. The sagittal suture between the two parietal foramina 

 is inclined to obliteration. 



The internal surface is concave; the deepest part is opposite 

 the parietal eminence, and is called the parietal fossa. This 

 surface is marked by grooves or canals for the meningeal vessels, 

 which run upward and backward from the anterior inferior 

 angle, from the middle and posterior portions of the inferior 

 border. A shallow half-groove runs along the superior border, 

 forming with that of the opposite side the channel for the 

 superior longitudinal sinus. In this half-groove is found the 

 internal opening of the parietal foramen when it exists. Near 

 the upper border of the bone are digital depressions for lodge- 

 ment of the Pacchionian bodies (modified tufts of arachnoid 

 membrane). 



The anterior border, 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 overlapped by the 

 squamous portion of the temporal; the posterior portion is 

 thick, and serrated by articulation with the mastoid portion of 

 the temporal. The anterior border, deeply serrated, is bevelled 

 at the expense of the outer surface above and of the inner 

 below; it articulates with the frontal bone, forming the coronal 

 suture. The posterior border, deeply denticulated, articulates 

 with the occipital, forming the lambdoid suture. 



The anterior superior angle, thin and pointed, corresponds 

 with that portion of the skull which in the fetus is membranous, 

 and is called the anterior fontanelle. The anterior inferior 

 angle is thin and lengthened, being received in the interval 

 between the great wing of the sphenoid and the frontal. Its 

 inner surface is marked by a deep groove, sometimes a canal, 

 for the anterior branch of the middle meningeal artery. The 

 posterior superior angle corresponds with the junction of the 

 sagittal and lambdoid sutures. In the fetus this is membranous 

 and forms a portion of the posterior fo7itanelle. The posterior 

 inferior angle articulates with the mastoid portion of the tem- 

 poral bone, the occipital. It generally presents on its inner 

 surface a small portion of the groove for the lateral sinus. 



