SPECIAL ANATOxMY. 143 



tlie orbital process of the frontal bone, externally to tbe 

 supra-orbital foramen, and through the lower part of the 

 malar bone. After which the separated portion of bone must 

 be raised by a chisel, and removed by division of the peri- 

 orbita,le. We are thus enabled to examine the lachrymal 

 gland, a racemose glandular body flattened from above 

 downwards, and moulded between the under surface of the 

 orbital process and the structures beneath ; it has also an 

 accessory lobule found in the upper eyelid. It resembles one 

 of the salivary glands in appearance, and pours its secretion 

 through several small ducts upon the inner surface of the 

 upper eyelid. After passing over the front of the eyeball, 

 being diffused by the winking action of the eyelids, the 

 tears (or lachrymal secretion) pass through the canal formed 

 by approximation of their free margins towards the inner 

 canthus, to which it is directed by the downward and inward 

 inclination of the palpebral fissure. By the caruncula lach- 

 rymalis it is directed into the puncta lachrymalia, openings 

 situated one at the inner extremity of each eyelid, and 

 from this passes through a series of membranous canals to 

 the anterior naris. It first gains the lachrymal canals, one 

 of which runs from each punctum in a downward direction ; 

 they converge and just at the lachrymal foramen meet and 

 form the lachrymal sac, from which the ductus ad nasum 

 runs through a special canal in the lachrymal and superior 

 maxillary bones. It may be exposed by use of the hammer 

 and chisel and will be found to extend for about three quar- 

 ters of its course in the bony canal. Its anterior part is 

 continued onwards between the bone and the Schneiderian 

 membrane as far as the anterior naris, where it opens at 

 the point of junction of the skin and mucous membrane 

 at the superior part. Situated between the caruncula 

 lachrymalis and the eyeball is the cartilage -nictitans 

 (winkingjmembrane, or third eyelid). It is thickest pos- 

 teriorly, and at its anterior free margin is covered by 

 mucous membrane, which generally contains some pigment. 

 Internally its yellow fibro-cartilaginous substance is con- 

 tinuous with some yellow elastic tissue, enclosed in the 

 meshes of which, and running among the muscles of the 

 eye, is fatty matter on ivhicli the movements of the cartilage 

 depend, for when, by the action of its muscles, the eyeball 

 is retracted it presses upon this mass of fat, which in its 

 turn presses the cartilage over the front of the eyeball. 



