THE FRONTAL BONE 



61 



The foramen is called the foramen caecum, and is generally closed below, but sometimes 

 transmits a vein from the nasal fossae to the superior sagittal (longitudinal) sinus. The frontal 

 crest serves for the attachment of the anterior part of the falx cerebri. On each side of the 

 middle line the bone is deeply concave, presenting depressions for the cerebral convolutions 

 and numerous snaall furrows which, running medially from the lateral margin, lodge branches of 

 the middle meningeal vessels. At the upper part of the surface, on either side of the frontal 

 sulcus, are some depressions for Pacchionian bodies. 



The horizontal portion consists of two somewhat triangular plates of bone 

 called the orbital plates, which, separated from one another by the ethmoidal 



Fig. 76. — The Frontal Bone. (Inferior view.) 

 Frontal spine 



Articulation with nasal 



bone 

 Articulation with max- 

 illa 

 Articulation with 

 lacrimal 



Trochlear fossa 

 Lacrimal fossa 

 Orbital surface 



Ethmoidal notch 



Articulation with 

 lamina papyracea 

 of ethmoid 

 Articulation with 



zygomatic 

 Articulation with 



greater wing of 



sphenoid 

 Articulation with 



lesser wing of 



sphenoid 



notch [incisura ethmoidalis], form the greater part of the roof of each orbit. When 

 the bones are articulated, the notch is filled up by the cribriform plate of the 

 ethmoid, and the half-cells on the upper surface of the lateral mass of the ethmoid 

 are completed by the depressions or half-cells which occupy the irregular margins 

 of the notch. Traversing these edges transversely are two grooves which com- 

 plete, with the ethmoid, the anterior and posterior ethmoidal canals. The 

 anterior transmits the anterior ethmoidal nerve and vessels; the posterior trans- 

 mits the posterior ethmoidal nerve and vessels, and both canals open on the 

 medial wall of the orbit. Farther forward, on either side of the nasal spine, are 

 the openings of the frontal sinuses, two irregular cavities which extend within 



Fig. 77. — The Frontal Bone at Birth. 



the bone for a variable distance and give rise to the superciliary arches (ridges). 

 Each is lined by mucous membrane and communicates with the nasal fossa by 

 means of a passage called the infundibulum. 



The inferior surface of each orbital plate, smooth and concave, presents im- 

 mediately behind the lateral angular process the lacrimal fossa, for the lacrimal 

 gland. Close to the medial angular process is a depression called the trochlear 

 fossa [fovea trochlearis], which gives attachment to the cartilaginous pulley for 

 the superior oblique muscle. The superior surface of each plate is convex and 

 strongly marked by eminences and depressions for the convolutions on the orbital 

 surface of the cerebrum. 



