1028 ORGANS OF THE SENSES AND THE COMMON INTEGUMENT 





In and near the fornices, but more plentiful in the upper than in the lower eyelid, 

 a number of convoluted tubular glands open on the surface of the conjunctiva. 

 Other glands, analogous to lymphoid follicles, and called by Henle trachoma glands, 

 are found in the conjunctiva, and, according to Strohmeyer, are chiefly situated 

 near the medial palpebral commissure. They were first described by Brush, in 

 his description of Peyer's patches of the small intestine, as "identical structures 

 existing in the under eyelid of the ox." 



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

 the medial palpebral commissure, and filling up the lacus lacrimalis. It consists 

 of a small island of skin containing sebaceous and sudoriferous glands, and is the 

 source of the whitish secretion which constantly collects in this region. A few 

 slender hairs are attached to its surface. Lateral to the caruncula is a slight semi- 

 lunar fold of conjunctiva, the concavity of which is directed toward the cornea; 

 it is called the plica semilunaris. Miiller found smooth muscular fibers in this fold; 

 in some of the domesticated animals it contains a thin plate of cartilage. 



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 

 "terminal bulb." 



The Lacrimal Apparatus (apparatus lacrimalis) (Fig. 896) consists of (a) the 

 lacrimal gland, which secretes the tears, and its excretory ducts, which convey the 

 fluid to the surface of the eye; (b) the lacrimal ducts, the lacrimal sac, and the naso- 

 lacrimal duct, by which the fluid is conveyed into the cavity of the nose. 



The Lacrimal Gland (glandula lacrimalis). The lacrimal gland is lodged in the 

 lacrimal fossa, on the medial side of the zygomatic process of the frontal bone. 

 It is of an oval form, about the size and shape of an almond, and consists of two 

 portions, described as the superior and inferior lacrimal glands. The superior 

 lacrimal gland is connected to the periosteum of the orbit by a few fibrous bands, 

 and rests upon the tendons of the Recti superioris and lateralis, which separate it 

 from the bulb of the eye. The inferior lacrimal gland is separated from the superior 

 by a fibrous septum, and projects into the back part of the upper eyelid, where 

 its deep surface is related to the conjunctiva. The ducts of the glands, from six 

 to twelve in number, run obliquely beneath the conjunctiva for a short distance, 

 and open along the upper and lateral half of the superior conjunctival fornix. 



Structures of the Lacrimal Gland (Fig. 897). In structure and general appearance the lacrimal 

 resembles the serous salivary glands (p. 1136). In the recent state the cells are so crowded with 

 granules that their limits can hardly be defined. They contain oval nuclei, and the cell proto- 

 plasm is finely fibrillated. 



The Lacrimal Ducts (ductus lacrimalis; lacrimal canals} . The lacrimal ducts, one 

 in each eyelid, commence at minute orifices, termed puncta lacrimalia, on the 

 summits of the papillae lacrimales, seen on the margins of the lids at the lateral 

 extremity of the lacus lacrimalis. The superior duct, the smaller and shorter of the 

 two, at first ascends, and then bends at an acute angle, and passes medialward 

 and downward to the lacrimal sac. The inferior duct at first descends, and then 

 runs almost horizontally to the lacrimal sac. At the angles they are dilated into 

 ampullae; their walls are dense in structure and their mucous lining is covered by 

 stratified squamous epithelium, placed on a basement membrane. Outside the 

 latter is a layer of striped muscle, continuous with the lacrimal part of the Orbic- 

 ularis oculi; at the base of each lacrimal papilla the muscular fibers are circu- 

 larly arranged and form a kind of sphincter. 



The Lacrimal Sac (saccus lacrimalis). The lacrimal sac is the upper dilated end 

 of the nasolacrimal duct, and is lodged in a deep groove formed by the lacrimal bone 

 and frontal process of the maxilla. It is oval in form and measures from 12 to 15 

 mm. in length ; its upper end is closed and rounded ; its lower is continued into the 

 nasolacrimal duct. Its superficial surface is covered by a fibrous expansion derived 



