THE FRONTAL BONE. 



195 



inner third of the arch is the supraorbital notch'' for the nerve and the artery of the 

 same name. The outer edge of the notch is more prominent than the inner. Very 

 often this is replaced by a foramen, which may be four or five milhmetres above the 

 edge of the bone. The arch ends externally in the external angular process, "" which 

 joins the malar and is very prominent. From it springs the temporal crest, ^ which, 

 curving upward and backward, separates the anterior surface of the bone from 

 the lateral one, which is a part of the temporal fossa. This crest generally, before 

 leaving the bone, divides into two lines, of which one is much more distinct than the 

 other. The vertical part of the bone has a slight point above in the middle and a 

 very jagged posterior border interlocking with the parietal. The latter is slightly 

 overlapped above and overlaps below. The bevelled, though jagged, articular sur- 

 face broadens below to meet a triangular rough space on the inferior surface. At the 

 lower lateral edge the bone is covered by the top of the great wing of the sphenoid. 



Fig. 220. 



Temporalis 



Temporal 



crest 

 Temporal 

 surface 



External angular 

 process 



Supra-orbital foramen 



Corrugator supercilii 



Orbicularis palpebrarum 



Nasal spine 



The frontal bone from before. 



The horizontal portion * shows in the middle of its lower aspect a rough surface 

 extending onto the front, called the nasal process, which articulates anteriorly with 

 the nasal bones and laterally with the ascending processes of the upper jaw. In the 

 middle projects a thin plate, the 7iasal spine, behind and between the nasal bones. 

 On either side of this there is often found a small smooth surface forming a small 

 part of the roof of the nasal cavity. Behind this lies the median ethmoidal notch,^ on 

 either side of which is an irregular space reaching to the inner edge of the orbit, 

 made of imperfect cells, completing the ethmoidal ones. In front of these a cavity 

 extends directly up, hollowing out the bone into \ki^ frontal sinus, which may extend 

 outward and backward over the orbits. A partition separates the sinuses of the two 

 sides, which are rarely symmetrical. The sinus opens into the middle meatus either 

 directly, under the front of the middle turbinate, or through the infundibulum. 

 When the ethmoid is in place, the cribriform plate and the crista galli fill up the 

 ethmoidal notch ; the ethmoidal cells are then closed, and the ethmoidal foramina 



1 Incisura supraorbitatis. - Processus zygomaticus. ° Linea temporalis. * Pars orbitaJis. ■' Incisura ethmoidalis. 



