168 SKELETON. 



ly downwards and outwards. Immediately within the orifice 

 the cavity is enlarged, owing to the projection of the orbitary 

 ridge of the os frontis, and the elevation of the anterior inferior 

 margin of the orbit, so that the greatest diameter is there ra- 

 ther vertical than horizontal. From this point the orbit de- 

 creases gradually in size to the sphenoidal fissure, or the supe- 

 rior foramen lacerum of the orbit which forms its apex. The 

 internal walls of the two orbits are nearly parallel, in conse- 

 quence of the cuboidal figure of the os ethmoides, which is 

 placed between them. 



The superior face or roof of the orbit is triangular and con- 

 cave : it is very thin, and presents but a slight septum between 

 the eye and the brain. Almost the whole of it is formed by the 

 orbitar process of the os frontis, its point only being made by 

 the little sphenoidal wing. The depression for the lachrymal 

 gland, at its external anterior part, is very perceptible. The 

 trochlea for the superior oblique muscle of the eye, is also well 

 seen about three-quarters of an inch above the point of the in- 

 ternal angular process of the os frontis. Just at the outer side 

 of this depression is the foramen or notch for the frontal artery 

 and nerve. The optic foramen may be seen, very readily, pass- 

 ing through the little wing of the sphenoid bone. 



The inferior face, or the floor of the orbit, is also triangular 

 and concave, and is formed by the orbitar process of the upper 

 maxillary bone principally; being assisted, however, at its an- 

 terior external margin, by a portion of the malar bone; and, at 

 its point behind, by the orbitar process of the palate bone. The 

 latter cannot be seen very distinctly in the articulated bones, 

 owing to its great depth in the orbit; but, when the external 

 side of the orbit is removed with a saw, its position is placed in 

 an interesting light. The floor of the orbit is thinner than its 

 roof, and forms a very slight separation from the maxillary sinus. 

 It is terminated behind by the spheno-maxillary fissure, or in- 

 ferior foramen lacerum of the orbit; a large slit, which, com- 

 mencing at the base of the sphenoidal fissure, separates the great 

 wing of the sphenoidal bone from the ethmoidal, the palate, and 

 the upper maxillary bones. This fissure runs obliquely out- 

 wards, so as to have its external extremity terminated by the 

 malar bone. Near the external extremity is seen the com* 



