THE APPENDAGES OF THE EYE. 



845 



lined by a layer of polyhedral cells. They are thus identical in structure with the 

 sebaceous glands. 



The conjunctiva is the mucous membrane of the eye. It lines the inner sur- 

 face 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 papillae, its deeper parts presenting a considerable amount 

 of lymphoid tissue. At the margin of the lids it becomes continuous with the 

 lining membrane of the ducts of the Meibomian glands, and, through the lachry- 

 mal canals, with the lining membrane of the lachrymal sac and nasal duct. At 

 the outer angle of the upper lid the lachrymal ducts open on its free surface ; 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 be- 

 comes thinner, loses its papillary structure, is transparent, and only slightly vas- 

 cular in health. Upon the cornea the conjunctiva consists only of epithelium, 

 constituting the anterior layer of the cornea (conjunctival epithelium) already 

 described (see page 826). Lymphatics arise in the conjunctiva in a delicate zone 

 around the cornea, from which the vessels run to the ocular conjunctiva. 



At the point of reflection of the conjunctiva from the lid on to the globe of the 

 eye, termed thefornix conjunctivas, are a number of mucous glands which are much 

 convoluted. They are chiefly found in the upper lid. Other glands, analogous to 



Puncta lachrymalia 



FIG. 453. The Meibomian glands, etc., seen from the inner surface of the eyelids. 



lymphoid follicles, and called by Henle trachoma glands, are found in the con- 

 junctiva, and, according to Strohmeyer, are chiefly situated near the inner can thus 

 of the eye. They were first described by Brush, in his description of Peyer's 

 patches of the small intestines, as " identical structures existing in the under eye- 

 lid of the ox." 



The nerves in the conjunctiva are numerous and form rich plexuses. According 

 to Krause, they terminate in a peculiar form of tactile corpuscle, which he terms 

 the "terminal bulb." 



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

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

 tion, the lacus lachrymalis. It consists of a small island of skin contain- 

 ing sebaceous and sweat glands, 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 toward the 



