FRONTAL BONE. 05 



Vertical Portion. Internal Surface (fig. 28). 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 edges afford attachment 

 to the falx cerebri. The crest terminates below at a small opening, the foramen 

 Cifcum, which is generally completed behind the ethmoid. This foramen varies 

 in size in different subjects, is usually 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 eminences and depressions for the 

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

 tions of the anterior meningeal arteries. Several small, irregular fossae are also 

 seen on either side of the groove, for the reception of the Pacchionian bodies. 



Fig. 28. Frontal Bone. Inner Surface. 



jornuny part rf Roirf fff tfose 



vntk 



Horizontal Portion; external Surface. This portion of the bone consists of 

 two thin plates, Avhich form the vault of the orbits, separated from one another by 

 the ethmoidal notch. Each orbital vault consists of a smooth, concave, triangular 

 plate of bone, marked at its anterior and external part, immediately beneath the 

 external angular process, by a shallow depression, the lachrymal fossa, for lodging 

 the lachrymal gland ; and at its 'anterior and internal part, by a depression, some- 

 times a small tubercle, for the attachment of the fibrous pulley of the Superior 

 oblique muscle. 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 edges transversely ; 

 5 



