LACHRYMAL APPARATUS. 627 



of the eyelids, and is reflected over the fore part of the sclerotic and cornea. In 

 each of these situations, its structure presents some peculiarities. 



The palpebral portion of the conjunctiva is thick, opaque, highly vascular, and 

 covered with numerous papillte, which, in the disease called granular lids, become 

 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 lachryrmil 

 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 palpebral 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 con- 

 junctiva is extremely thin and closely adherent, and no vessels 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 adult they pass only 

 to the circumference of the cornea. 



The caruncula lacrymalis is a small, reddish, conical-shaped body, situated 

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

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

 structure to the Meibornian, 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 caruncula 

 is a slight 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. 310). 



The lachrymal apparatus consists of the lachrymal gland, which secretes the 

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



Fig. 310. The Lachrymal Apparatus. Right Side. 



This fluid is carried away by the lachrymal canals into the lachrymal sac, ana 

 along the nasal duct into the cavity of the nose. 



