PARIETAL BONE. 47 



tubercle of the neural spine. The occipital bone articulates with 

 eight bones — the parietals, squamosals, petrosals, sphenoid, and 

 the atlas. 



PARIETAL BONE. 

 (Fig. 10. n. J 12. 2.) 



These bones are situated at the superior and lateral parts of 

 the cranium, of -which they form the walls and part of the roof 

 The parietal is a large thin bone, possessed of an external and 

 ^n internal surface, and four borders. 



The external surface is convex and smooth. On each side of 

 the sagittal suture, formed by the junction of the two parietal 

 bones, there is a curved ridge, to which the temporalis muscle is 

 attached ; these ridges together form an angle, the point of which 

 joins the occipital crest. The lateral parts of this surface are 

 roughened, to articulate with the squamosal bone. 



The internal surface is concave, and marked by numerous 

 grooves and indentations, which correspond with the convolutions 

 of the brain. A groove, termed the longitudhval groove, and 

 generally formed by a ridge or crest, runs along the junction of 

 the two bones, and gives lodgment to the longitudinal sinus of 

 the dura mater ; this crest terminates posteriorly in a three-sided 

 process, the parietal protuberance or ossific tentorium, to which, 

 as well as to the crest, is attached the falx cerebri, a part of the 

 dura mater which contains the above-named sinus. In front of 

 this process the longitudinal groove ends in two transverse grooves, 

 which lodge the transverse sinuses of the dura mater, and are 

 continued down to the parieto-temporal conduit, a passage formed 

 between this bone and the temporal. 



The posterior border of this bone is thick and denticulated, 

 and articulates with the occipital ; the anterior' border is slightly 

 concave and strongly serrated, articulating with the frontal bone ; 

 the internal border is denticulated^ and united to its fellow of 

 the opposite side, forming the saggital suture ; the exte^nial 

 border is divided by a prominent angle into two parts, the 

 anterior one being thin, and articulating with the squamosal, 

 while the posterior is thicker, and articulates with the petrosal 

 Ijone, the prominent angle or crest meeting the sphenoid bone. 



Sometimes the sagittal suture is interrupted or rendered bifid 

 posteriorly by the insertion of a small bone, generally triangular 



