

THE FRONTAL BONE 



137 



The crest ends below in a small notch which is converted into a foramen, the fora- 

 men cecum, by articulation with the ethmoid. This foramen varies in size in 

 different subjects, and is frequently impervious; when open, it transmits a vein 

 from the nose to the superior sagittal sinus. On either side of the middle line the 

 bone presents depressions for the convolutions of the brain, and numerous small 

 furrows for the anterior branches of the middle meningeal vessels. Several small, 

 irregular fossae may also be seen on either side of the sagittal sulcus, for the 

 reception of the arachnoid granulations. 



Orbital or Horizontal Part (pars orbitalis). This portion consists of two thin 

 triangular plates, the orbital plates, which form the vaults of the orbits, and are 

 separated from one another by a median gap, the ethmoidal notch. 



Supraorbital 

 foramen 





With maxilla 



With nasal- >\l \ Undcr mr f ar e of nasal p 

 With perpendicular plate of ethmoid || f orm i ng part of roof of 



FIG. 135. Frontal bone. Inner surface. 



Surfaces. The inferior surface (Fig. 135) of each orbital plate is smooth and 

 concave, and presents, laterally, under cover of the zygomatic process, a shallow 

 depression, the lacrimal fossa, for the lacrimal gland; near the nasal part is a depres- 

 sion, the fovea trochlearis, or occasionally a small trochlear spine, for the attach- 

 ment of the cartilaginous pulley of the Obliquus oculi superior. The superior 

 surface is convex, and marked by depressions for the convolutions of the frontal 

 lobes of the brain, and faint grooves for the meningeal branches of the ethmoidal 

 vessels. 



The ethmoidal notch separates the two orbital plates; it is quadrilateral, and 

 filled, in the articulated skull, by the cribriform plate of the ethmoid. The margins 

 of the notch present several half-cells which, when united with corresponding 

 half-cells on the upper surface of the ethmoid, complete the ethmoidal air cells. 

 Two grooves cross these edges transversely; they are converted into the anterior 



