LACHRYMAL APPARATUS. 



693 



covered with numerous papillae, which in the disease called granular lids, be- 

 come greatly hypertrophied. At the margin of the lids, it becomes continuous 

 with the lining membrane of the ducts of the Meibomian glands, and, through 

 the lachrymal canals, with the lining membrane of the lachrymal sac and nasal 

 duct. At the outer angle of the upper lid, it may be traced along the lachrymal 

 ducts into the lachrymal gland ; and at the inner angle of the eye, it forms a 

 semilunar fold, the plica semilunaris. The folds formed by the reflection of the 

 conjunctiva from the lids on to the eye are called the superior and inferior pal- 

 pebral folds, the former being the deeper of the two. Upon the sclerotic, the 

 conjunctiva is loosely connected to the globe; it becomes thinner, loses its 

 papillary structure, is transparent, and only slightly vascular in health. Upon 

 the cornea, the conjunctiva is extremely thin and closely adherent, and no ves- 

 sels can be traced into it in the adult in a healthy state. In the foetus, fine 

 capillary loops extend, for some little distance forwards, into this membrane ; 

 but in the 7/iult, they pass only to the circumference of the cornea 



The carwncula lachrymalis is a small, reddish, conical-shaped oody, situated 

 at the inner canthus of the eye, and filling up the small triangular space in this 

 situation, the lacus lachrymalis. It consists of a cluster of follicles similar in 

 structure to the Meibomian, covered with mucous membrane, and is the source 

 of the whitish secretion which constantly collects at the inner angle of the eye. 

 A few slender hairs are attached to its surface. On the outer side of the carun- 

 cula is a light semilunar fold of mucous membrane, the concavity of which is 

 directed towards the cornea ; it is called the plica semilunaris. Between its two 

 layers is found a thin plate of cartilage. This structure is considered to be the 

 rudiment of the third eyelid in birds, the membrana nictitans. 



LACHRYMAL APPARATUS. (Fig. 375.) 

 The Lachrymal Apparatus consists of the lachrymal gland, which secretes 



Fig. 375. The Lachrymal Apparatus. Eight Side. 



the tears, and its excretory ducts, which convey the fluid to the surface of the 

 eye. This fluid is carried away by the lachrymal canals into the lachrymal 

 sac, and along the nasal duct into the cavity of the nose. 



The lachrymal gland is lodged in a depression at the outer angle of the orbit, 

 on the inner side of the external angular process of the frontal bone. It is of 

 an oval form, about the size and shape of an almond. Its upper convex sur- 

 face is in contact with the periosteum of the orbit, to which it is connected by 

 a few fibrous bands. Its under concave surface rests upon the convexity of the 

 eyeball, and upon the Superior and External Eecti muscles. Its vessels and 



