36 



THE BONES OF THE HEAD. 



grooves, running from the anterior inferior angle, is sometimes converted into a 

 canal for a short distance. A slight depression along the inner part of the superior 

 border forms, with the one of the opposite side, the groove of the longitudinal sinus ; 

 and a depression at the posterior inferior angle forms a small part of the groove 

 of the lateral sinus. Near the upper border there are in most skulls, but particularly 

 in those of old persons, small irregular pits, lodging the Pacchionian bodies. 



Borders. The anterior, superior, and posterior borders are deeply serrated. The 

 inferior border presents in the greater part of its extent a sharp or squamous edge, 

 with a slightly fluted surface directed outwards, and overlapped at its anterior 

 extremity by the great wing of the sphenoid, and behind that by the squamous part 



TEMP. SURF. 



TEMP. CREST 



EXT. ANG. PROC. 



Fig. 36. FRONTAL BONE, FROM BEFORE. (Drawn by D. Gunn.) f 



of the temporal bone ; its posterior part is serrated, and articulates with the mastoid 

 portion of the temporal. The anterior border is slightly overlapped by the frontal 

 bone above, but overlaps the edge of that bone below. 



Varieties. The parietal foramen varies greatly ; frequently it is absent on one or both 

 sides ; in extreme cases it has been seen more than half an inch in diameter. As a rare 

 occurrence the parietal bone is divided by a suture into an upper and a lower part. In senile 

 bones considerable depressions of the outer surface are sometimes met with, the floor of which 

 is not thicker than paper ; usually on both sides and symmetrical (Humphry, Med. Chir. 

 Trans., 1890). 



THE FRONTAL BONE. 



The frontal bone, arching upwards and backwards above the orbits, forms the 

 fore part of the cranium ; it likewise presents inferiorly two thin horizontal laminse, 

 the orMtal plates, which form the roofs of the orbits, and are separated by a median 

 excavation, the ethmoidal notch. It articulates with twelve bones, viz., posteriorly 

 with the parietals and sphenoid ; outside the orbits with the malars ; and between 



