196 



HUiMAN ANATOMY. 



and canals are formed. External to this lies the orbital plate, the front of which is 

 overhung by the supraorbital arch. It is slightly concave from side to side. Just 

 under cover of the external angle is an ill-marked dep7-eSsion ' for the lachrymal gland. 

 Near the internal angular process there may be a small fossa " for the cartilaginous 

 pulley for the superior oblique muscle. More frequently there is a minute tubercle. 

 The inner border of the orbital surface runs nearly straight backward. Its sharp 

 edge articulates from before backward with the ascending process of the maxilla, 

 the lachrymal, and the ethmoid. The outer edge runs obliquely inward. External 

 to it, behind the angular process which joins the malar, is a rough triangular surface 

 articulating with the great wing of the sphenoid. The posterior border of the orbital 

 plate is short and serrated to join the small wings of the sphenoid. 



The internal surface of the frontal presents ihe frontal crest below in the 



Fig. 221. 



Groove for longitudinal 

 sinus 



Pacchionian 

 depressions 



Meningeal 

 grooves 



External angular process 



With great 

 wing of 

 sphenoid 



With lesser 



wing 

 With malar 



Supra-orbital foramen 



Frontal sinus 



Frontal crest 

 Foramen cseeum 



Nasal spine 

 Nasal process 



The frontal bone from behind. 



median line. It is a slight ridge, to which the falx is attached. A narrow groove 

 runs along it, starting at the forameyi ccecum, a hole either in this bone or between 

 it and the ethmoid. This groove is for the superior longitudinal sinus. After a 

 short distance the crest disappears, but the groove broadens and extends to the top 

 of the bone. There are a few grooves for branches of the middle meningeal artery 

 at the side and some small Pacchionian depressions.^ Below, on either side of the 

 notch, are the orbital plates, which slant strongly downward and inward, so as to 

 leave the ethmoid in a deep gutter. Their upper surfaces are very irregular with 

 so called digital impressions for the opposed cerebral convolutions. It is now evident 

 how the frontal, the ethmoid, and the lesser wings of the sphenoid form the anterior 

 fossa of the skull. 



'See Parietal Bone (page 198). 



' Fossa elandulae lacrlmalis. ' Fovea trochlearis. 



