38 



THE BONES OF THE HEAD. 



median ridge, which is continued into a sharp process of variable length, the nasal 

 spine. The latter descends in the septum of the nose, between the crest of the nasal 

 bones in front and the vertical plate of the ethmoid behind. Between the 

 ethmoidal notch and the inner margin of the orbital surface is an irregular area 

 occupied by depressions forming the roofs of cells in the ethmoid bone. Traversing 

 this surface are two grooves, which complete, with the ethmoid, the anterior 

 and posterior internal orbital canals ; the anterior transmits the nasal nerve and the 

 anterior ethmoidal vessels ; the other, the posterior ethmoidal vessels. Farther 

 forward is the opening of the frontal sinus, a cavity which extends within the bone 

 for a variable distance behind the superciliary ridges. Outside and behind the 



LONGITUDINAL SULCUS 



PACCHIONIAN DEPRESSIONS 



Fig. 39. FRONTAL BONE, FROM BEHIND. (Drawn by D. Gnnn.) 



orbital surface there is a large rough triangular area which articulates with the great 

 wing of the sphenoid. 



Cerebral surface. This surface forms a large concavity, except over the roofs 

 of the orbits, which are convex. Upon it are seen the impressions of the cerebral 

 convolutions, which, with the intervening ridges, are strongly marked over the orbits. 

 A groove, the frontal sulcus, lodging the superior longitudinal sinus, descends from the 

 middle of the upper margin of the bone, and is succeeded by the frontal crest, a ridge 

 which runs down nearly to the lower margin. A small foramen, usually formed in 

 part by the crista galli of the ethmoid, is situated at the base of the frontal crest ; 

 it is known as the foramen caecum, being generally closed below, but it may transmit 

 a minute vein from the nasal fossae. On each side small ramifying furrows, which 

 lodge branches of the middle meningeal vessels, run inwards from the lateral margin 

 of the bone ; and at the upper part, in the neighbourhood of the longitudinal groove, 

 are some depressions for Pacchionian bodies. The upper and greater part of 

 the edge encompassing the cerebral surface of the bone is serrated, and articulates 



