THE EYE. 329 



which numerous blood-vessels and nerves pass ; behind this, 

 and covering the whole extent of the lid, are bundles of the 

 orbicularis palpebrarum ; some small fasciculi of this muscle 

 are also found at the lower and inner angle of the lid, enclosing 

 the openings of the Meibomian glands. These bundles, known 

 as the musculus ciliaris Riolani, have fibres which are among 

 the smallest of the striped variety of muscular tissue. 



Behind this layer is a thin sheet of loose connective tissue, 

 which merges without any sharp boundary line into the tar- 

 sus ; this latter body forms a leaf-shaped plate about twenty 

 millimetres in length by one millimetre in thickness, and is 

 composed of very dense connective-tissue fibres separated only 

 by minute lymph-spaces ; it has few blood-vessels or nerves, 

 and serves to give the requisite stiffness to the looser tissues of 

 the Ud. 



The Meibomian glands are imbedded in the tarsus. Their 

 excretory ducts, which are directed at right angles to the pal- 

 pebral margin, have their openings on the surface of the lid 

 near its posterior angle. They are lined with epithelium, which 

 at the external orifice is similar to that in the superficial parts 

 of the skin ; more internally it is serrated, while in the acini of 

 the gland it has a cuboidal shape. These glands have a straight 

 central tube, around which the acini are clustered, and into 

 which they discharge the sebum, a material composed of epi- 

 thelial cells that have undergone fatty degeneration. This 

 oleaginous substance serves to moisten the edges of the lid and 

 to prevent the overflow of tears. 



Above the Meibomian glands, and in part imbedded in the 

 tarsus, are the acinous glands, which have their openings on 

 the surface of the conjunctiva fornicis. Above these glands 

 the smooth muscular fibres of the little palpebralis muscle of 

 Muller are inserted, through a tendon, into the upper part of 

 the tarsus ; the fibres of this muscle are quite large and have 

 peculiar irregular cells with pigmented nuclei scattered 

 throughout them. 



To prepare sections from the lids they should be pinned fiat 

 on a piece of cork and then immersed in Muller' s fluid' for 

 eight days. After being washed in water they are placed in 

 absolute alcohol until sufficiently hard ; or they may be hard- 



1 See chapter on General Methods. 



