Henry Gray (18251861). Anatomy of the Human Body. 1918.
has a vertical diameter of about 5 mm. The free or ciliary margins of these plates are thick and straight. The attached or orbital margins are connected to the circumference of the orbit by the orbital septum. The lateral angles are attached to the zygomatic bone by the lateral palpebral raphé. The medial angles of the two plates end at the lacus lacrimalis, and are attached to the frontal process of the maxilla by the medial palpebral ligament (page 381).
The orbital septum (septum orbitale; palpebral ligament) is a membranous sheet, attached to the edge of the orbit, where it is continuous with the periosteum. In the upper eyelid it blends by its peripheral circumference with the tendon of the Levator palpebræ superioris and the superior tarsus, in the lower eyelid with the inferior tarsus. Medially it is thin, and, becoming separated from the medial palpebral ligament, is fixed to the lacrimal bone immediately behind the lacrimal sac. The septum is perforated by the vessels and nerves which pass from the orbital cavity to the face and scalp. The eyelids are richly supplied with blood.
FIG. 892 Front of left eye with eyelids separated to show medial canthus. (See enlarged image)
The Tarsal Glands (glandulæ tarsales [Meibomi]; Meibomian glands) (Fig. 895).The tarsal glands are situated upon the inner surfaces of the eyelids, between the tarsi and conjunctiva, and may be distinctly seen through the latter on everting the eyelids, presenting an appearance like parallel strings of pearls. There are about thirty in the upper eyelid, and somewhat fewer in the lower. They are imbedded in grooves in the inner surfaces of the tarsi, and correspond in length with the breadth of these plates; they are, consequently, longer in the upper than in the lower eyelid. Their ducts open on the free magins of the lids by minute foramina.
FIG. 893 Sagittal section through the upper eyelid. (After Waldeyer.) a. Skin. b. Orbicularis oculi. b. Marginal fasciculus of Orbicularis (ciliary bundle). c. Levator palpebræ. d. Conjunctiva. e. Tarsus. f. Tarsal gland. g. Sebaceous gland. h. Eyelashes. i. Small hairs of skin. Sweat glands. k. Posterior tarsal glands. (See enlarged image)
Structure.The tarsal glands are modified sebaceous glands, each consisting of a single straight tube or follicle, with numerous small lateral diverticula. The tubes are supported by a basement membrane, and are lined at their mouths by stratified epithelium; the deeper parts of the tubes and the lateral offshoots are lined by a layer of polyhedral cells.
The conjunctiva is the mucous membrane of the eye. It lines the inner surfaces of the eyelids or palpebræ, and is reflected over the forepart of the sclera and cornea.