THE ORBITS. 



FlG. 12. 



THE ORBITS. 



Describe the Orbital Cavities. The orbits are 2 conoidal cavities, 

 situated between the forehead and the face, their bases outwards, their apices 

 pointing backwards, the lines of axial prolongation meeting at the sella 

 turcica of the sphenoid bone. They contain the organs of vision with their 

 appendages, and are each formed by 7 bones, the frontal, 1 ethmoid, 2 sphe- 

 noid, 3 * 5 lachrymal, 6 superior maxillary, 7 palate, 8 and malar, 9 of which the 

 first three are common to both orbits. Each orbit communicates with I cavity 

 and 4 fossae, as follows, viz. 



Cavity of the cranium, by the optic foramen u and sphenoidal fissure. 10 

 Fossa (4) the nasal, temporal, zygomatic, and spheno-maxillary, by the 



nasal duct 12 and the spheno-maxillary fissure. 13 



What Foramina communicate with each orbit ? Nine, the optic 

 foramen, 11 sphenoidal fissure, 10 anterior 21 and posterior 22 ethmoidal foramina, 

 supraorbital, 14 infraorbital, 15 and malar foramina, 16 the nasal duct, 12 and the 

 spheno-maxillary fissure. 13 



Describe the Roof of the Orbit. Formed by the orbital plate of the 

 frontal bone anteriorly, 1 and the 

 lesser wing of the sphenoid 4 pos- 

 teriorly, it is concave, and presents 

 the 



Lachrymal Fossa, 11 at its outer 



angle,for the lachrymal gland. 



Depression, 18 at the inner angle, 



for the pulley of the superior 



oblique. 



Describe the Floor of the 

 Orbit. Formed by the orbital 

 surface of the superior maxillary 

 bone, 7 and the orbital process of 

 the malar 9 and palate bones, 8 it 

 is nearly flat and presents the 

 Palato-maxillary Suture poste- 

 riorly. 



Infraorbital Canal, and a De- 

 pression for the superior 

 oblique muscle of the eye, 

 anteriorly. 



Infraorbital Groove} 9 poste- 

 riorly. 

 3* 



