36 OSTEOLOGY, OR ANATOMY OF OSSEOUS SYSTEM 



the parietal bone, and forms, by this union, the lambdoid 

 suture. The inferior border extends from the lateral to the 

 inferior angle; its upper half is rough, and articulates with 

 the mastoid portion of the temporal, forming the mastooccipital 

 suture; the inferior half articulates with the petrous portion 

 of the temporal, forming the petrodccipital suture; these two 

 portions are separated from each other by the jugular process. 

 In front of this process is a deep notch, which, with a similar 

 one on the petrous portion of the temporal, forms the foramen 

 lacerum posterius, or jugular foramen. This notch is occa- 

 sionally subdivided into two parts by a small process of bone, 

 and it generally presents an aperture at its upper part, the 

 internal opening of the posterior condyloid foramen. 



The superior angle is received into the interval between 

 the posterior superior angles of the two parietal bones; it 

 corresponds with that part of the skull in the fetus which is 

 called the posterior fontanclle . The inferior angle is represented 

 by the square-shaped surface of the basilar process. At an 

 early period of life a layer of cartilage separates this part of 

 the bone from the sphenoid, but in the adult the union between 

 them is osseous. The lateral angles correspond to the outer 

 ends of the transverse grooves, and are received into the interval 

 between the posterior inferior angles of the parietal and the 

 mastoid portion of the temporal. 



The Parietal Bones 



The two parietal bones together form the median portion 

 of the roof and sides of the skull. Each is roughly quadri- 

 lateral, and presents two surfaces (external and internal), 

 four borders, and four angles. 



The external surface is convex, smooth, and near its centre 

 is an eminence called the parietal eminence, or boss. This is 

 very prominent in young bones. 



Through or just below this are the superior and inferior 

 temporal lines, -f inch apart; to the superior one is attached 

 the temporal fascia; to the inferior, the temporal muscle; 

 below it is the temporal surface for origin of the temporal muscle. 

 Near the upper border, and f inch (2 cm.) from the posterior 

 angle, the parietal foramen is often found. It is for the exit 

 of a vein, and usually the entrance of a branch of the occipital 



