172 



THE SKELETON. 



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 ramifications 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. 



Horizontal Portion. External Surface. This portion of the bone consists of 

 two thin plates, which form the vault of the orbit, 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 



With superior maxillary^ 



With nasal. 

 With perpendicular plate of ethmoid. 



FIG. 136. Frontal bone. 



Frontal sinus. 



\Under surf ace of nasal process, 

 forming part of roof of nose. 



Inner surface. 



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 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 

 edges transversely ; they are converted into canals by articulation with the ethmoid, 

 and are called the anterior and posterior ethmoidal canals : they open on the inner 

 wall of the orbit. The anterior one transmits the nasal nerve and anterior 

 ethmoidal vessels, the posterior one the posterior ethmoidal vessels. In front of 

 the ethmoidal notch, on either side of the nasal spine, are the openings of the 

 frontal sinuses. These are two irregular cavities, which extend upward and 

 outward, a variable distance, between the two tables of the skull, and are 

 separated from one another by a thin, bony septum. They give rise to the 



