THE PARIETAL BONE. 



197 



Articulations. — The frontal articulates with the nasal, superior maxillary, 

 lachrymal, malar, ethmoid, sphenoid, and parietal bones. 



Development and Changes. — The only important centres are the two sym- 

 metrical ones appearing- in the membrane at the frontal eminences towards the end 

 of the second month of foetal life. There is a separate point for the nasal spine 

 and one near each angular process of the orbit. These smaller ones are fused in the 

 seventh month of foetal life. There is a centre for the posterior angle (Gegenbaur), 

 which also unites before birth. The median {inetopic) suture usually closes towards 

 the end of the second year, and a year or two later is hardly to be recognized, except 

 by the rudiment at the lower end. Occasionally the suture persists ; in that case it 

 remains in extreme old age after the others have vanished. Not very rarely in 

 the foetus or infant a dilatation of the fissure, metopic fontanelle, is found near the 

 upper part of its lower third. There are a few cases of traces of this in the adult.' 

 The frontal sinuses appear about the seventh year and increase up to adult life. 

 Later they are said to grow again, since in the latter part of life the inner table of 

 the skull follows the shrinking brain. As their size is dependent chiefly on the 

 behavior of the inner table, we can infer little about it from the shape of the fore- 

 head, unless the superciliary eminences are very prominent. 



THE PARIETAL BONE. 



The two parietal bones ^ complete the vault of the skull. Each is a thin quadri- 

 lateral bone with an inner and an outer table separated by diploe. Near the middle 



Fig. 222. 



Parietal foramen 



Post. sup. angle <K.. % 



Ant. sup. angle 



Posterior inferior angle 



Anterior inferior angle 



Mastoid 



Right parietal bone, outer surface. 



Sphenoid 



on the convex external surface \s \.\\q parietal eminence ;' where ossification begins. 



It is very prominent in childhood, but, as a rule, is not very evident in the adult. 



Crossing this surface below the middle are two curved lines * continuous with those 



^Schwalbe: Zeitschrift fiir Morph. und Anthrop., Bd. iii., 1901. 



* Ossa parietalia. ^ Tuber parietale. ■* Linae temporalcs 



