THE FRONTAL BONE. 



63 



Internal Surface (Fig. 29). Along the middle line is a vertical groove, the 

 edges of which unite below to form a ridge, the frontal crest ; the groove lodges 

 the superior longitudinal sinus, whilst its margins afford attachment to the falx 

 cerebri. The crest terminates below at a small notch which is converted into a 

 foramen by articulation with the ethmoid. It is called the foramen cceeum, and 

 varies in size in different subjects : it is sometimes partially or completely 

 impervious, lodges a process of the falx cerebri, and when open transmits a vein 

 from the lining membrane of the nose to the superior longitudinal sinus. On 

 either side of the groove the bone is deeply concave, presenting depressions 

 for the convolutions of the brain, and numerous small furrows for lodging the 

 ramifications of the anterior meningeal arteries. Several small, irregular fossae 

 are seen also on either side of the groove, for the reception of the Pacchionian 

 bodies. 



Horizontal Portion. This portion of the bone consists of two thin plates, 

 the orbital plates, which form the vault of the orbit, separated from one 

 another by a median gap, the ethmoidal notch. The external surface of each 

 orbital plate consists of a smooth, concave, triangular lamina of bone, marked 

 at its anterior and external part (immediately beneath the external angular 



With superior maxillary. 



With nasal 



Frontal sinus. 



\Under surface of nasal process, 

 With perpendicular plate of ethmoid. " forming part of roof of nose. 



FIG. 29. Frontal bone. Inner surface. 



process) by a shallow depression, the lachrymal fossa, for lodging the lachrymal 

 gland; and at its anterior and internal part by a depression (sometimes a small 

 tubercle), the trochlear fossa, for the attachment of the cartilaginous pulley of the 

 Superior oblique muscle of the eye. The ethmoidal notch separates the two orbital 

 plates ; it is quadrilateral, and filled up, when the bones are united, by the 

 cribriform plate of the ethmoid. The margins of this notch present several half- 

 cells, which, when united with corresponding half-cells on the upper surface of the 

 ethmoid, complete the ethmoidal cells ; two grooves are also seen crossing these 



