THE FKONTAL BONE. 



ethmoid. On each side of the root of this process the nasal part of the bone 

 is grooved obliquely from above downwards and forwards, and enters into the 

 formation of the narrow roof of the nasal cavity. Anteriorly the nasal notch 

 is limited by a rough, U-shaped serrated surface, the medial part of which 

 articulates with the nasal bones, whilst on each side the frontal processes of the 

 maxillae are united with it. Behind this, amid the broken cells, the passages 

 leading into the frontal sinuses are readily distinguished, and here the medial 

 edges of the orbital plates articulate with the lacrimal bones. The orbital part 

 is thin and brittle. Anteriorly, it is bounded by the supraorbital margin, just within 

 which, midway between the medial angular process and the supraorbital notch, there 

 is a Small shallow depression (fovea trochlearis), often displaying a spicule of bone 

 arising from its edge (trochlear spine), which affords attachment to the pulley of 

 the superior oblique muscle of the eyeball. Laterally, the orbital part is overhung by 

 the supraorbital margin and the zygomatic process, and in the hollow so produced 

 (fossa glandulce lacrimalis) the lacrimal gland is lodged. The extremity of the 

 zygomatic process articulates with the frontal process of the zygomatic bone 



For articulation with 

 small wing of sphenoid 



Foveolse 

 granu lares 



Sagittal sulcus and attach- 

 ment of falx cerebri 



Groove for meningeal artery 



Orbital surfac 



Temporal surface 



Zygomatic process (O.T. 

 Lateral angular) 



Surface for articula- 

 tion with great wing 

 of sphenoid 



Fossa for the lacrimal 

 gland 



Ethmoidal foramina 



Ethmoidal notcl 



Frontal sinus 



Nasal surface 



Supraorbital notch 

 Trochlear pit 



Nasal notch 



Frontal spine 

 FIG. 129. THE FRONTAL BONE AS SEEN FROM BELOW. 



Behind this the irregular edge of the orbital surface is united with the great wing 

 of the sphenoid by a triangular area, which also extends on to the inferior aspect 

 of the temporal surface of the frontal bone. The apex of the orbital surface, 

 for the space of about half an inch, articulates with the small wing of the sphenoid. 

 The cerebral surface of the bone forms a fossa in which lie the anterior and 

 inferior parts of the frontal lobes of the cerebrum, the gyri of which impress their 

 form on the inner table of the bone. Here, too, on each side of the median plane, 

 may be seen depressions, called foveolae granulares, for the lodgment of arachnoideal 

 .granulations (O.T. Pacchionian bodies). Descending from the centre of the upper 

 margin of the bone is a median groove, the sagittal sulcus ; narrowing below, this 

 ends in a ridge the frontal crest which nearly reaches the anterior part of the 

 ethmoidal notch, where it terminates in a small orifice, the foramen caecum, placed 

 usually in the suture between the anterior part of the ethmoid and the frontal. 

 This foramen may, or may not, transmit a small vein from the nose to the com- 

 mencement of the superior sagittal sinus. This sinus, which is interposed between 

 the layers of the falx cerebri, is at first attached to the frontal crest, but subse- 

 quently occupies the sagittal sulcus. Deeply concave from side to side and from 

 above downwards, the lateral parts of the fossa are seen to be traversed by small 

 grooves for the anterior branches of the middle meningeal arteries. Below, the 



