THE EYE. 



of conjunctiva, the plica semilunaris (fig. 1, Ps), which rests on the eyeball ; whilst 

 occupying the recess of the angle at the border of this fold, is a spongy-looking 

 reddish elevation (caruncula lacrimalis, Car) formed by a small isolated portion 

 of skin containing a few large modified sweat glands, as well as a group of sebaceous 

 glands which open into the follicles of very fine hairs. There is further found in it 

 a small amount of plain muscular tissue (H. Miiller), as well as some cross-striated 

 muscular fibres. A few plain muscular fibres are also to be found in the plica 

 semilunaris. 



The plica semilunaris is the rudiment of the third eyelid (membrana niclitans] 

 found in many animals ; and in some animals, and occasionally in man, the carun- 

 cula lacrimalis retains its connection with the skin at the inner canthus. The 

 muscular tissue of the nictitating membrane of animals, and presumably, therefore, 

 of the semilunar fold of man, receives its nerve supply through the cervical sympa- 

 thetic. In many animals, and occasionally in man (in the negro constantly, accord- 

 ing to Griacomini), the plica semilunaris contains a plate of hyaline cartilage. 



Structure of the lids. The skin covering the eyelids is thin and delicate, and 

 covered with fine downy hairs (fig. 2, i, i). These are provided with sebaceous 

 follicles ; small sweat-glands are also present. At the line of the eyelashes the skin 

 joins the conjunctival mucous membrane which lines the inner surface of the lids. 

 The cutis vera contains a number of ramified pigment cells, and pigment is also 

 frequently found in the Malpighian layer of the epidermis, especially near the inner 

 angle of the lids. Beneath the skin is a quantity of very loose connective tissue, 

 entirely free from fat and containing the fasciculi of the orbicularis palpebrarum 

 muscle (&), and beneath the mucous membrane on the posterior surface is the 

 lamina of dense connective tissue before mentioned, and known as the tarsus (e), or 

 from its consistence, the tarsal cartilage, which thins off near the attached margin 

 of the eyelid into the palpebral fascia connecting it with the margin of the orbit. 

 In the tarsi are imbedded the Meibomian glands (/). In the upper eyelid there is, 

 in addition, the insertion of the levator palpebrae superioris, attached to the upper 

 or anterior surface of the tarsus by fibrous tissue and smooth muscular tissue (see 

 below) and further sending a well-marked flat tendinous expansion, the bundles of 

 which pass between the bundles of the orbicularis palpebrarum muscle, and are 

 attached to the skin of the middle of the eyelid (fig. 6). There is nothing corre- 

 sponding to this in the lower lid, but the inferior rectus and oblique muscles send 

 strands of fibrous tissue forwards to be attached to the tarsus and palpebral ligament. 



The orbicularis muscle is attached to the skin by loose subcutaneous connec- 

 tive tissue, but glides loosely on the tarsal cartilages. A marginal fasciculus lies 

 within the line of the eyelashes, separated by the bulbs of the lashes from the other 

 fibres, and constituting the ciliary bundle or muscle of Riolan (b 1 ). The fibres of 

 the orbicularis are very small and pale in colour. Its attachments have already 

 been described in Yol. II., Part 2. 



The tarsi (tarsal cartilages) are two thin elongated plates formed of dense 

 connective tissue, without any intermixture of cartilage-cells. They are placed one in 

 each lid, to which they give shape and firmness. The upper one, the larger, is half 

 oval in form, being broader near the centre and narrowing towards the angles of 

 the lids. The lower is thinner, much narrower, and more nearly of a uniform 

 breadth throughout. Their free edges, which are straight, are thicker than any 

 other part. At the inner canthus they are fixed to the nasal process of the superior 

 maxillary bone by the internal tarsal slip ; and at the outer angle are attached to 

 the malar bone by a fibrous band termed the outer tarsal ligament (Yol. II., p. 281). 

 Groups of fat-cells are found in the tarsus both near its attached border and 

 scattered over its anterior surface (Merkel). 



