THE LACHRYMAL APPARATUS. 



909 



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 consists only of epithelium, constituting the anterior layer of the cornea 

 (conj unc rival epithelium) already described (see page 893). 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 the/"/-///'./- njunctivce, are a number of mucous glands which are much 

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



Piincta lachrymalia. 



FIG. 537. 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 canthus 

 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 lachrymaUs 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 lachrymdti*. 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 caruncula is a slight 

 semilunar fold of mucous membrane, the concavity of which is directed toward the 

 cornea : it is called the plica semilunaris. Miiller found smooth muscular fibres 

 in this fold, and in some of the domesticated animals a thin plate of cartilage has 

 been discovered. This structure is considered to be the rudiment of the third eyelid 

 in birds, the membrana nictitans. 



The Lachrymal Apparatus (Fig. 538). 



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. 

 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 



