1026 ORGANS OF THE SENSES AND THE COMMON INTEGUMENT 





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 palpe- 

 bral raphe". 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 orbilale; 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 



Punctum lacrimale 



Plica semllunaris 



Caruncula 



Punctum lacrimale 



Openings of tarsal 



glands 



Fia. 892. Front of left eye with eyelids separated to show 

 medial canthus. 



by its peripheral circumference with the tendon 

 of the Levator palpebrse superioris and the 

 superior tarsus, in the lower eyelid with the infe- 

 rior 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. 



The Tarsal Glands (glandules 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 dis- 

 tinctly 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, con- 

 sequently, longer in the upper than in the lower eyelid. Their ducts open on the 

 free magins of the lids by minute foramina. 



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 palpebrse, and is reflected over the forepart of the sclera and cornea. 



FIG. 893. Sagittal section through the upper 

 eyelid. (After Waldeyer.) a. Skin. b. Orbicularis 

 oculi. b'. Marginal fasciculus of Orbicularis (ciliary 

 bundle), c. Levator palpebrse. d. Conjunctiva. 

 e. Tarsus. /. Tarsal gland, g. Sebaceous gland. 

 h. Eyelashes, t. Small hairs of skin. Sweat 

 glands, k. Posterior tarsal glands. 



