OSTEOLOGY. 21 



obliquus superior; superior, inferior, internal and external recti. 

 Its OSSIFIC CENTRES are fourteen, as follow : Body, 2 anterior and 

 2 posterior; external pterygoid plates and greater wings, 2; in- 

 ternal pterygoid plates, 2; lingula, 2; lesser wings, 2; spheno- 

 turbinals, 2. 



THE ETHMOID is a spongy, cubical bone, consisting of a 

 perpendicular lamella, a horizontal or cribriform plate, and two 

 lateral masses. 



The horizontal or cribriform plate presents from before 

 backward the following points: 



Tiro projections completing the foramen ccecum^ the com- 

 mencement of the longitudinal sinus; 



Crista galli, affording attachment to the falx cerebri; 



Foramina cribrosa, three rows, transmitting filaments of 

 the olfactory body; 



Fissure for passage of the nasal branch of the ophthalmic 

 nerve. 



The pcrjicudicular plate assists in forming the nasal septum, 

 articulating in front with the crest of the nasal bones and the 

 frontal bone and behind with the sphenoid and vomer. It is 

 usually inclined to one side. 



'I 1 ! ie lateral masses are composed of the ethmoidal cells. 



The upper surface presents two notches, converted into fo- 

 ramina by articulation with the frontal bone 



The anterior ethmoidal foramen, transmitting the anterior 

 ethmoidal artery and nasal nerve, and 



The posterior ethmoidal foramen, transmitting the posterior 

 ethmoidal artery and vein. 



The outer surface presents 



The 05 planum, a smooth plate of bone forming the inner 

 wall of the orbit, and projecting downward from it is 



The unciform process, a hook-like plate of bone closing the 

 upper part of the opening of the antrum. 



The inner surface forms part of the nasal fossa, and presents 



The sHjirriur inrbinuted bone, forming the upper boundary 

 of the superior meatus, into which open the sphenoidal and pos- 

 terior ethmoidal cells, and the 



Middle- liirhimiled bone, forming the upper boundary of the 

 middle meatus of the nose, into which open the anterior eth- 

 iiioidal cells, the frontal cells through the infundibulum, and the 

 ant rum Highmoriaimm. 



It articulates with fifteen bones two sphenoidal turbinated, 

 sphenoid, frontal, and eleven of the face, the two nasal, two 

 lachrymal, two superior maxilla 1 , two palate, two inferior turbi- 

 nated, and the vomer. 



