Henry Gray (18251861). Anatomy of the Human Body. 1918.
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 Peyers 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 semilunar fold of conjunctiva, the concavity of which is directed toward the cornea; it is called the plica semilunaris. Müller 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 nasolacrimal 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 protoplasm 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 papillæ 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 ampullæ; 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 Orbicularis oculi; at the base of each lacrimal papilla the muscular fibers are circularly 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