142 



THE SKELETON. 



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 orbits, separated from one another 



Fig. 95. Frontal Bone. Inner Surface. 



ith 



with Perpendieul-ar vla.te of Ethmoid 



base of Nasal Spine, 

 vy part rf Roof tf Nase 



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 (sometimes 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 ; they are converted into canals by 

 articulation with the ethmoid, and are called the anterior and posterior ethmoidal 

 canals ; they open on the inner walls 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 is the nasal spine, a sharp- 

 pointed eminence, which projects downwards and forwards, and articulates in 

 front with the crest of the nasal bones ; behind, it is marked by two grooves, 

 separated by a vertical ridge ; the ridge articulates with the perpendicular 

 lamellae of the ethmoid, the grooves form part of the roof of the nasal fossae. 

 On either side of the base of the nasal spine are the openings of the frontal 

 sinuses. These are two irregular cavities, which extend upwards and outwards, 

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



