THE EYELIDS AND CONJUNCTIVA 



735 



THE EYELIDS AND CONJUNCTIVA 

 The eyelids, upixT and lower (Palpebra superior et inferior), arc movable 

 folds of integument situated in front of the ej'eball. When closed, they cover the 

 entrance to the orbit and the anterior surface of the eyeball. Tiu^ upper lid is 

 much more extensive and more movable than the lower one, and its free edge is 

 more concave. The interval between the lids is termed the palpebral fissure (Rima 

 palpebrarum). When the eye is closed, it is an oblique slit about two inches (ca. 

 5 cm.) in length; when open, it is bicon- 

 vex in outline. The ends of the fissure 

 are the angles or canthi, and are dis- 

 tinguished as internal or nasal, and 

 external or temporal (Angulus oculi 

 medialis, lateralis) . The external angle 

 is rounded when the eye is open, but 

 the internal angle is narrowed to form 

 a ID -shap(Hl bay or recess, termed the 

 lacrimal lake (Lacus lacrimalis). In 

 this there is a rounded, pigmented 

 jirominence known as the lacrimal 

 caruncle (Caruncula lacrimalis) ; it is 

 about the size of a small pea and is 

 covered with modified skin, connected 

 with that of the inner commissure, 

 from which project a num])er of hairs 

 provided with sebaceous glands. The 

 lids unite on either side and form the 

 commissures, internal and external 

 (Commissura palpebrarum medialis, 

 lateralis). The anterior surface of 

 the lids (Facies anterior palpebrarum) 

 is convex and presents a variable num- 

 ber of long tactile hairs in addition to 

 the ordinary but very short hairs. A 

 consideral)le number of tactile hairs 

 are scattered over the lower part of 

 the lower hd, but on the upper lid 

 they are ver}^ scanty. The infrapal- 

 pebral depression (Sulcus infrapal])e- 

 bralis) indicates somewhat indistinctly 

 the limit of the lower lid. The upper 

 lid is marked loy two funxjws when 

 raised. The posterior surface (Facies 

 postcn'ior palpebrarum) is adapted to 

 the free surface of the eyeball and is 



covered by the palpebral conjunctiva. Th(> free border of th(> lid is smooth and 

 usually black. It has a well-defined posterior margin (Liml)us pal])ebralis pos- 

 terior), along which the ducts of the tarsal glands open. Tlie anterior margin 

 (Limbus palpebralis anterior) bears stiff hairs termed the cilia or eyelashes. On 

 the upper lid the cilia are long and numerous except at its inner third, -where 

 they are very 'small or absent. On the lower lid the cilia are often scarcely 

 distinguishable from the ordinary hairs; in other cases they may be clearlj^ seen 

 except near the external canthus, and are much finer and shorter than those of 

 the upper lid. The edge of each lid is pierced n(>ar the internal angle by a 



Fi( 



'7 3 



552. — Vertical Section of Anterior Part of 

 Eye of Horse, with Lids Half Closed. 

 1, Tarsal gland of upper lid; 2, palpebral con- 

 junctiva; 3, fornix coiijunctiwT; 4, levator palpebra- 

 superioris; 5, orbicularis oculi; ff, cornea; 7, anterior 

 chamber; 8, iris; 9, 9', granula iridis, 10, posterior 

 chamber; 11, ciliary process; 12, ciliary mviscle; 13, 

 < iliary zone or svispensory lig. of lens; 14, chorioid; 15, 

 sclera; 16, lens; 17, root of tactile liair. (After Bayer, 

 Augenheilkunde.) 



