312 ANIMAL PHYSIOLOGY. [LESSON 96. 



when this occurs they produce a form of blindness for which there 

 is no remedy. 



1415. Amongst other tissues which enter into the composition 

 of the eye-lids, are two thin lamellae of fibro-cartilage, called the 

 tarsal cartilages, which give form and support to the eye-lids. 



1416. Between "these cartilages, and embedded in them, lie the 

 Meibomian glands, so called from Meibomius, their discoverer. 

 They consist of a long duct, which opens upon the edge of the eye- 

 lids, surrounded by a cluster of follicles, which conceal the tube, ex- 

 cept at its terminal portion. As these glands extend the whole width 

 of the cartilages, they are necessarily longer in the upper than the 

 under eye-lid ; they differ in number in the two lids, there being 

 twenty-four in the upper and thirteen in the lower lid. 



1417. These glands secrete a fatty matter, and may be regarded 

 as a form of sebaceous glands. Their chief function appears to be 

 to keep the margins of the eye-lids soft (greasy), and prevent adhesion. 

 They can at all times be well seen upon the inner surface of the lids, 

 shining and glistening like so many rows of pearls (Fig. 444). In 



Fitt. 444. 



Meibomian glands, in situ. 



composition they consist of a lengthened tube, or duct, which extends 

 from one end of the gland to the other. On either side a number 

 of small follicles are found, so densely clustered as to entirely con- 

 ceal the duct, except at its termination. The tarsal cartilages are 

 grooved for the reception of these glands, which are retained in their 

 place by a layer of cartilage, which folds over each gland, and another 

 similar layer, which folds over the former. By lifting up these two 

 folds, a gland can be easily lifted out of the groove in the lower 

 cartilage, not being in any way attached to it. An enlarged figure 

 of a gland, so obtained, is shown in Fig. 445; when magnified, 



