OSSA PARIETALIA. 



65 



transverse arched ridge, ge- Fig. 12.* 



nerally of a whiter color 

 than any other part of the 

 bone ; from which, in bones 

 that have strong prints of 

 muscles, we see a great many 

 converging furrows, like so 

 many radii drawn from a 

 circumference towards a cen- 

 tre. From this ridge of each 

 bone the temporal muscle 

 rises : and, by the pressure of its fibres, occasions the furrows 

 just now mentioned. Below these we observe, near the semi- 

 circular edges, a great many risings and depressions, which are 

 joined to like inequalities on the inside of the temporal bone, 

 and form the squamous suture. Near the upper edges of these 

 bones, towards the hind part, is a small hole in each, through 

 which a vein passes from the teguments of the head to the lon- 

 gitudinal sinus.f o 



On the inner concave surface of the parietal bones we see a 

 great many deep furrows, disposed somewhat like the branches 

 of trees : the furrows are largest and deepest at the lower edge 

 of each os parietale, especially near its anterior angle, where a 

 complete canal is sometimes formed. 



[These furrows are made by the ramifications of the great 

 middle artery of the dura mater: they have been commonly 

 attributed to the pulsation of the artery causing the absorp- 

 tion of the bone, but it is more probable that the deposition of 

 the bone has been prevented where the artery beats, and thus 

 the bone becomes modelled over the artery in the same way 

 that it is made to conform to the surface of the brain. If it 



* The external surface of the left parietal bone. 1 . Superior or sagittal border. 

 2. Inferior or squamous border. 3. Anterior or coronal border. 4. Posterior or 

 lambdoidal border. 5. The temporal ridge. The figure is situated immediately 

 over the parietal protuberance. 6. The parietal foramen, unusually large. 

 7. The anterior inferior angle. 8. The posterior inferior angle. 



f It transmits, also, an artery from the integuments to the dura inater, and 

 is called the parietal foramen. p. 



6* 



