THE EYEBALL AXD ITS SURROUXDINGS 



841 



to the free inar<iin of the lid — the Meil)onii;in follicles. The conjunctiva over the 

 outer and inner fourths of each lid is not (juite so smooth as elsewhere, and is nor- 

 mally of a deeper red colour; we shall find later that there are glands well devel- 

 oped in these positions. 



When the eyelids are opened naturally, we see through the ])alpebral aj)erture 

 the following: the greater part of the transparent cornea, and behind it the coloured 

 iris with the pu])il in its centre; white sclerotic to the outer and inner sides of the 

 cornea; the semilunar fold and lachrymal caruncle at the inner canthus. The 

 extent of the eyel>all visible in this way varies according to its i)osition. Thus, 

 with the eyes looking straight forwards, the loAver margin of the upper lid is nearly 

 opposite to the top of the cornea, or, more strictly, to a line mithvay between the 

 top of the cornea and the ujiper l)order of the pupil, while the lower lid corresponds 

 with the lower corneal margin. When the eyes are directed strongly upwards, the 

 ui)per lid is relatively on a slightly higher level, as it is simultaneously raised, but 

 the lower lid now leaves a strip of sclerotic exposed below the cornea. On looking 

 downwards the upper lid covers the upper part of the cornea as low down as the 

 le\el of the top of the pupil, while the lower lid is about midway between the pupil 

 and the lower corneal l)order. 



If we draw the eyelids forcibly apart, we expose the whole cornea, and a zone 

 of sclerotic al)out eight and a half millimetres in ])readth above and below, and ten 

 millimetres in l)readth to the outer and inner sides, altogether about one-third of 



Fig. 472. 



-View of Evkball, ktc, obtained on drawing the Lids fokciblv apart. 

 (After Merkel, slightly modified.) 



SEMILUNAR FOLD -Sfc-/' 

 UPPER LACHRYMAL PUNCTU.i 

 CARUNCLE 

 LOWER LACHRYMAL PUNCTUM 



OPENINGS OF MEIBOMIAN FOLLICLES 



CONJUNCTIVAL FORNIX 



the globe; all the eyeball thus exposed is covered l)v the ocular conjunctiva. Over 

 the sclerotic the conjunctiva is freely movable, and through it we see superficial 

 l)lood- vessels that can be made to slip from side to side along with it (conjunctival 

 vessels). Occasionally otiier deeper vessels may also be seen which do not move 

 with the conjunctiva, l)ut are attached to the sclerotic (anterior ciliary arteries and 

 veins). Near the corneal border the conjunctiva ceases to be freely movable, and 

 it is closely adherent to the whole anterior surface of the cornea, giving the latter 

 its characteristic bright, reflecting appearance; no blood-vessels are visible through 

 it here in health. (\\'hen the lids are shut, the space enclosed between their pos- 

 terior surfaces and the front of the eycljall is thus everywhere covered by conjunc- 

 tiva, and is known as the conjunctival sac. ) 



Not infrecjuently, the tendinous insertions of some or all of the recti muscles 

 into the sclerotic may be seen through the conjunctiva, each insertion appearing as 

 a series of Avhitish parallel lines running towards, but terminating aliout seven 

 millimetres from the corresponding corneal border. The cornea appears as a 

 transparent dome, having a curvature greater than that of the sclerotic; the 

 junction of the two unecjually curved surfaces is marked by a shallow depression 

 nmning around the cornea, known as the scleral sulcus. In outline the cornea 

 is nearly circular, but its horizontal diameter is slightly greater than its vertical. 

 Between it and the iris a space exists, whose depth we can estimate roughly by 

 looking at the eye from one side ; this si)ace, or anterior chamber, is occupied by 



