584 



THE EYE. 



The fibres of the orbicularis muscle ; loose connective tissue ; the so 

 called tftrsal cartilages, together "with a thin fibrous membrane, the 

 palpebral ligament, which attaches them to the margin of the orbit ; 

 and, finally, the ]\Ieibomian glands. In the upper eyelid there is, in 

 addition, the insertion of the levator palpebral superioris, in the form 

 of a fibrous expansion attached to the upper or anterior surface of the 

 tarsal cartilage. 



Fig. 396. 



Fig. 396. — Vertical Section of the Left Orbit and its Contents. 

 The section has been carried first obliquely tliroiigh the middle of the optic foramen 

 and optic nerve as far as the back of the eyeball, and thence forward through the eyeball, 

 eyelids, &c. a, frontal bone ; b, superior maxillary ; c, eyebrow ; d, the upper, and d', 

 the lower eyelid, partially open, showing the section of the tarsal cartilages, the eyelashes, 

 &c. ; c, e, the reflection of the conjunctiva from the upper and lower eyelids to the sur- 

 face of the eyeball ; /, the levator palpebrte superioris muscle ; g, the upper, g', the 

 lower rectus muscle ; k, the inferior oblique muscle divided ; 1, 1, the optic nerve 

 divided in its sheath ; 2, the cornea ; 2', the sclerotic ; 3, aqueous chamber ; 4, crystal- 

 line lens ; 5, vitreous chamber. 



The orlicularis 7nuscle is closely adherent to the skin by fine connec- 

 tive tissue entirely devoid of fat, but glides loosely on the tarsal carti- 

 lages. A marginal fasciculus lies within the line of the eyelashes, 

 separated by the bulbs of the lashes from the other fibres, and con- 

 stituting the nmsculus ciliaris Riolani. 



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

 dense connective tissue, without, according to most observers, any inter- 

 mixture of cartilage-cells. They are placed one in each lid, and serve 

 to give shape and firmness to those parts. The upper cartilage, 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 an uniform breadth throughout. Their free or 

 ciliary edge, which is straight, is thicker than any other part. At 

 the inner canthus they are fixed by fibrous slips of the tendon of the 

 orbicularis muscle ; and at the outer angle are attached to the malar 

 bone by a fibrous band belonging to the palpebral ligament, and named 

 the external tarsal ligament. 



The palpehral ligament is a fibrous membrane placed beneath the 



