68 



A MANUAL OF ANATOMY 



inwards. It forms a right angle with its fellow of the opposite 

 side, and abuts against the great wing of the sphenoid. The 

 internal border is directed from before backwards, is parallel with 

 its fellow of the opposite side, and forms the lateral boundary of 

 the ethmoidal notch. It is bevelled at the expense of the lower 

 plate, and the bevelled surface presents several excavations, which 

 close in the ethmoidal cells on the upper border of the lateral 

 mass of the ethmoid. This surface is crossed by two transverse 

 grooves, anterior and posterior, which, with similar grooves on the 

 contiguous part of the ethmoid, form the anterior and posterior 

 ethmoidal (internal orMtal) canals. These open on the inner wall 



Nasal Spine 



Ala 



For Nasal Process of 

 Superior Maxilla ^ 



Frontal Sinus 



Trochlear Fossa 



Frontal Crest and Ethmoidal Notch 



Nasal Notch 



Groove for Ant. Ethmoidal Canal 

 Supra-orbital Notch 



Orbital Plate 

 / 

 ' Lachrymal Fossa 



Ext. Angular Process 



Surf, for Great 

 Wing of Sphenoid 



For Small Wing 

 of Sphenoid 



Groove for Posterior 

 Ethmoidal Canal 



Parietal Border 



Fig. 46. — The Frontal Bone (Inferior View). 



of the orbit, and the anterior gives passage to the nasal nerve and 

 anterior ethmoidal vessels, whilst the posterior transmits the posterior 

 ethmoidal vessels and spheno- ethmoidal nerve. The truncated 

 apex of the orbital plate articulates with the small wing of the 

 sphenoid. 



In front of the anterior ethmoidal groove on either side is the 

 opening of the frontal air sinus. Each leads into a cavity within 

 the bone, which extends outwards from near the middle line for 

 a variable distance behind the superciliary ridge. The sinuses are 

 separated by a median septum, and may be unilocular or multi- 

 locular. In the latter case the subdivisions may extend back- 



