126 SKELETON. 



partition. They communicate with the cavity of the nose 

 through the anterior ethmoidal cells. 



With the exception of the inferior part, where the processes 

 and sinuses exist, the os frontis is of a very uniform thickness, 

 and the diploic or cellular structure is found constantly be- 

 tween its external and internal faces. 



This bone is united to the parietal, ethmoidal, and sphenoi- 

 dal of the cranium; and to several bones of the face. 



2. Parietal Bones, (Ossa Parietalia, Os Parietaux.) 



These bones, it has been stated, form the superior and lateral 

 parts of the middle of the cranium. They are quadrilateral, 

 convex externally, and concave internally. Their external and 

 internal tables are uniformly separated by a diploic structure, 

 which, from being more abundant at the superior part of the 

 bones, occasions there an increased thickness. 



The external surface of the parietal bone is raised about its 

 middle into the parietal protuberance. Just below this protu- 

 berance is an arched, rough, broad, but slightly elevated ridge, 

 marking the origin of the temporal fascia and muscle, and 

 continuous with the ridge on the side of the frontal bone. 

 The internal surface of the bone is marked by the convolutions 

 of the brain ; there are also a number of furrows upon it, hav- 

 ing an arborescent arrangement, and produced by the ramifi- 

 cations of the middle artery of the dura mater. These furrows 

 all proceed from two large ones at the anterior arid at the infe- 

 rior part of the bone: not unfrequently at the latter point these 

 furrows are converted into perfect tubes, by the deposition of 

 bone all around the arteries. Of these furrows, the foremost 

 may be traced from the greater wing of the sphenoidal bone, 

 and running somewhat parallel with the anterior margin of the 

 parietal; and the other passing from the squamous portion of 

 the temporal, is a little behind the middle of the parietal, and 

 inclines towards its posterior superior angle. The internal 

 face of the parietal bone also presents an imperfect fossa at its 

 superior margin, which is completed by junction with its fel- 

 low, and accommodates the longitudinal sinus of the dura ma- 

 ter. Near this edge it is not uncommon to see one or more 



