LACRYMAL ORGANS. 



81 



Internal structure of the eyelids. The tar- 

 sal cartilages may be looked upon as the skele- 

 ton of the eyelids, and the membraneous ex- 

 pansion intervening between them and the mar- 

 gins of the orbits as connecting ligaments. The 

 latter, indeed, are called the tursal ligaments, 

 although they do not in reality possess a liga- 

 mentous structure, but consist merely of dense 

 laminar cellular membrane. On the inner sur- 

 face of the tarsal cartilages and tarsal ligaments 

 the palpebral conjunctiva adheres. On the 

 outer surface are the palpebral and ciliary por- 

 tions of the orbicularis palpebrarum muscle, over 

 which is the skin. Moreover, incorporated 

 with the superior tarsal ligament is the expan- 

 sion of the tendon of the levator palpebrce supe- 

 rioris muscle. Imbedded in the substance of 

 the tarsal cartilages lie the Meibomian follicles. 

 Underneath the skin and the ciliary portion of 

 the oroicularis palpebrarum muscle, the roots of 

 the eyelashes lie close on the tarsal cartilages. 



Tursat* cartilages. Tarsi; Fr., Les Tarses; 

 Ital., I tarsi; Germ., l)er Aiigenliedknorpel, 

 These are thin plates of nbro-cartilage, convex 

 on the outer surface, concave on the inner, to 

 be adapted to the front of the eyeball. The 

 upper is the larger. One of their margins is 

 thick and straight, the other thin and curved, 

 especially so in the upper, which therefore re- 

 presents in some degree a segment of a circle, 

 whilst the lower is little more than a narrow 

 stripe. The thick and straight margin, called 

 the ciliary, forms the margin of the eyelid; the 

 thin and curved margin, called orbital, degene- 

 rates into the membraneous expansion already 

 mentioned under the name of tarsal ligaments. 

 Towards the outer canthus the orbital margins 

 of the tarsal cartilages run into the ciliary ones 

 at an acute angle, whilst towards the inner can- 

 thus they form an obtuse angle by their junc- 

 tion. The transverse length of the tarsal carti- 

 lages is somewhere about an inch, the breadth 

 of the upper cartilage at its broadest part about 

 one-third of an inch, the breadth of the lower 

 cartilage only half as much. At the inner can- 

 thus the tarsal cartilages extend no farther than 

 the lacrymal points, and at the outer canthus 

 they stop close to the commissure of the two 

 lids. 



As to the intimate composition of the tarsal 

 cartilages, they consist of what is called fibro- 

 cartilage, a microscopically fibrous substance, 

 without any of the corpuscles of common carti- 

 lage. 



In the human lower eyelid, the thickness of 

 this substance is inconsiderable, and its con- 

 sistence not so great as in the upper. In the 

 lower animals it is in the same state in both 

 eyelids. This is what has led Zeissf to say 

 that he never found a real cartilaginous tarsus 

 in the human lower eyelid, nor among the lower 

 mammifera in the upper eyelid either. " In 



Tarsus, propter siccitatem quod carnis sit ex- 

 pers. 



t Anatomische Untersuchungen der Meibomis- 

 chen Drusen des Menschen und der Thieren mil 

 besondere Berucksichiigung ihrer Verhaltniss zum 

 larsus. In Ammon's Zeitschrift der Ophthalmo- 

 logie. Bd. iv. p. 249. 

 VOL. III. 



the sow only," says he, " there is a nearer ap- 

 proach to a tarsal cartilage than is to be found 

 in any other of the lower animals." Miiller* 

 has very well explained away all this difference 

 of opinion, by showing that the dense cellular 

 tissue which, according to Zeiss, occupies the 

 place of tarsal cartilage in the human lower 

 eyelid, and in both those of the inferior mammi- 

 fera, is the same tissue, as the more consistent 

 nbro-cartilage of the human upper eyelid, only 

 in a less condensed state. 



The Meibomian glands are commonly de- 

 scribed as being situate between the palpebral 

 conjunctiva and tarsal cartilage. Winslow, 

 Haller, and Zinn describe them as lying in 

 grooves on the posterior surface of the tarsal 

 cartilages. The Meibomian glands are seen 

 very distinctly from the inside of the eyelids, as 

 if they were immediately underneath the con- 

 junctiva. But if the skin and orbicularis muscle 

 be removed from the outside, these glands be- 

 come equally visible there. " Where, then," 

 asks Zeiss,f " do they lie, before or behind 

 the tarsal cartilage ?" Examination of sections 

 of the cartilage shows that the Meibomian glands 

 lie in the substance of the tarsal cartilage itself; 

 and in the human lower eyelid and in both 

 those of the lower animals, in the less consistent 

 fibrous structure which there composes the 

 tarsus. 



At the outer canthus the cellulo-membra- 

 neous expansions called tarsal ligaments are 

 stronger, and form bands which decussate and 

 thus tie the tarsal cartilages to each other and 

 to the outer margin of the orbit. These bands 

 compose what is called the external palpebral 

 ligament. 



The internal palpebral ligament is the tendon 

 of the orbicularis palpebrarum muscle, tendo 

 oculi, or tendo palpebrarum. This, to adopt 

 the description of Professor Harrison of Dub- 

 lin, " is a small horizontal tendon, nearly one 

 quarter of an inch in length. It is inserted in- 

 ternally into the upper end of the nasal process 

 of the superior maxillary bone ; thence it passes 

 outwards and backwards to the internal com- 

 missure of the eyelids, where it forks into two 

 slips which enclose the caruncula lacrymalis, 

 and are then inserted each into the tarsal carti- 

 lage and the lacrymal duct."J 



Orbicularis palpebrarum muscle. This is de- 

 scribed in the article FACE, vol.ii. p. 221. Here 

 we shall only advert to some particular points 

 in its history. The fibres of the orbicularis 

 pertaining to the upper eyelid arise from the 

 internal angular process of the frontal bone, and 

 from the upper edge of the tendo palpebrarum, 

 and proceed, forming a curve, at first upwards 

 and outwards, and then downwards and out- 

 wards, within the upper eyelid and along and 

 over the upper edge of the orbit towards the 

 temple and outer angle of the eye. Here they 

 meet those of the lower eyelid which have come 

 from the nasal process of the upper jaw-bone, 



* Archiv, 1836. Jahresbericht, p. xxxviii. 



t L. c. p. 240, and op. cit. Bd. v. S. 216. See 

 also Sichel in Lancette Francaise, Gazette des Ho- 

 pitaux, No. 53, 55, and 57. Paris, 1833. 



t Dublin Dissector, 4th ed. p. 6. 



G 



