72 PRACTICAL ANATOMY. 



palate. As the frontal, ethmoid, and sphenoid are com- 

 mon to both cavities, the two orbital cavities together are 

 formed of but eleven bones. At the apex of the orbit 

 is the optic foramen, which transmits the optic nerve 

 and ophthalmic artery. External to this is the anterior 

 lacerated foramen, a triangular opening directed upward 

 and outward. It transmits the third, fourth, ophthalmic 

 division of the fifth, and sixth pair of nerves, and the 

 ophthalmic vein. It communicates with the spheno- 

 maxillary fissure, which passes outward and downward 

 from the inner portion of the foramen lacerum anterius. 

 The roof of the orbit is strongly concave, and is formed 

 by the horizontal plate of the frontal, and, posteriorly, 

 the under surface of the lesser wing of the sphenoid. 

 The outer wall, directed obliquely outward and forward, 

 is formed by the great wing of the sphenoid and the malar 

 bone. The inner wall, directed backward, slopes slightly 

 downward and outward, is formed principally by the 

 lachrymal and ethmoid. The floor, slightly concave, is 

 formed by the superior maxillary, malar, and palate. The 

 orbital cavities contain the eyes and their muscular ap- 

 paratus, and afford these delicate organs protection from 

 injury by the strong and prominent orbital ridge which 

 forms the circumference of the cavity. 



The nasal cavities are placed in the middle of the 

 face, between and below the orbits. They have open- 

 ings anteriorly and posteriorly. The anterior opening is 

 somewhat heart-shaped, the apex being above ; the pos- 

 terior openings, two in number, are elliptical, their long 

 axes are directed vertically, and they open into the 

 pharynx. Owing to the absence of the triangular car- 

 tilage in the prepared skull, the anterior opening is not 

 divided. The nasal are two wedge-shaped cavities, sepa- 

 rated from each other by the vertical plate of the eth- 



