1116 



THE ORGANS OF SPECIAL SENSE 



(Fig. 823), the smaller of the two, is thinner and of an elliptical form. The free or ciliary 

 margin of these plates is thick, and presents a perfectly straight edge. The attached or orbital 

 margin is connected to the circumference of the orbit by the fibrous membrane of the lids, with 

 which it is continuous. The outer anyle of each plate is attached to the malar bone by the ex- 

 ternal tar sal ligament (licjamentum palpebralis lateralis) (Fig. 823). The inner angles of the 

 two plates terminate at the commencement of the lacus lacrimalis; they are attached to the nasal 

 process of the superior maxilla by the internal tarsal ligament or the tendo oculi (ligamentum 

 palpebrale mediate) (Fig. 823). In reality these so-called ligaments are fascial expansions situated 

 one in each lid, and are attached marginally to the edge of the orbit, where they are continuous 



with the periosteum. The superior ligament 

 blends with the tendon of the Levator palpe- 

 brae, the inferior with the inferior tarsal plate. 

 Externally, the superior and inferior ligaments 

 fuse to form the external tarsal ligament just 

 referred to; internally they are much thinner, 

 and, becoming separated from the internal tarsal 

 ligament, are fixed to the lacrimal bone imme- 

 diately behind the lacrimal sac. The whole 

 fascial sheet spanning the orbit, and reenforced 

 by these ligaments, constitutes the orbital sep- 

 tum (septum orbitale), which is perforated by 

 the vessels and nerves which pass from the 

 orbital cavity to the face and scalp. 



The Meibomian or Tarsal Glands 



(glandulae tarsales [Meibomi]) (Figs. 824 

 and 826) are situated in the tarsal plates, 

 and may be distinctly seen through the 

 conjunctiva on everting the eyelids, pre- 

 senting the appearance of parallel strings 

 of pearls. They are about thirty in 



number in the upper eyelid, and some- 

 what fewer in the lower. They corre- 

 spond in length with the breadth of each 

 plate, and are, consequently. longer in 

 the upper than in the lower eyelid. Their 

 ducts open on the free margin of the lids 

 by minute foramina, which correspond in 

 number to the follicles. The use of their 

 secretion is to prevent adhesions of the 

 lids. 



FIG. 824. Vertical section through the upper eye- 

 lid, a. Skin. 6. Orbicularis palpebrarum. 6'. Mar- 

 ginal fasciculus of Orbicularis (ciliary bundle), c. 

 Levator palpebrae. d. Conjunctiva, e. Tarsal plate. 

 /. Meibomian gland, g. Sebaceous gland, h. Eye- 

 lashes, i. Small hairs of skin. j. Sweat-glands. 

 k. Posterior tarsal glands. (After Waldeyer.) 



Structure. These glands are a variety of the 

 cutaneous sebaceous glands, each consisting of 

 a single straight tube or duct, having a cecal 

 .termination, and with numerous small alveoli 

 opening into it. The tubes consist of basement 

 membrane, lined at the mouths of the tubes by 



stratified epithelium; the deeper parts of the tubes and the alveoli are filled with polyhedral 



cells. They are thus identical in structure with the sebaceous glands. 



The Conjunctiva (Figs. 825 and 826) is the mucous membrane of the eye. It 

 lines the inner surface of the eyelids, is reflected over the fore part of the sclera 

 and cornea, and joins the lids to the eyeball. In each of these situations its struc- 

 ture presents some peculiarities. 



The palpebral portion (tunica conjunctiva palpebrarum) (Fig. 826) of the con- 

 junctiva lines the posterior surface of the lids. It is thick, opaque, highly vascular, 

 and covered with numerous papilkie, its deeper parts presenting a considerable 

 amount of lymphoid tissue. At the margins of the lids it becomes continuous 



