THE EYELIDS. 



359 



and behind with the conjunctiva. The tarsal plates lodge the linear series 

 of the Meibomian or tarsal glands. These structures, between twenty 

 and thirty in number in the upper lid and about one third less in the lower 

 one, consist of a chief tubular duct, placed vertically and lined by stratified 

 squamous epithelium, which is beset with numerous simple or branched, 

 irregular, flask-shaped alveoli. The latter contain cuboidal epithelial ele- 

 ments that resemble in appearance and condition those found in sebaceous 

 follicles, to which class, in fact, the tarsal glands belong. They secrete an 



Skin 



Subcutaneous tissue 



Orbicularis palpebrarum 

 Fat 



Tarsal muscle 



Levator palpebra: 



superioris 



Meibomian gland 

 Conjunctiva 



Artery of tarsal arch 



Meibomian duct 



Glands of Moll " fcilia ^Ciliary bundle 

 FIG. 409. Sagittal section of upper eyelid of child. X 15. 



oily substance, sebum palpebrarum^ which is discharged through the minute 

 punctiform orifices of the ducts seen as a row of dark points just external 

 to the sharp conjunctival border of the eyelid. In this manner the latter is 

 kept lubricated, and thus, under usual conditions, maintains an effective 

 barrier against the overflow of the tears from the conjunctival sac. Within 

 the free edge of the eyelids, just in advance of the tarsal plates, lie the 

 glands of Moll and the glands of Zeiss, The former are coiled tubules, 

 resembling modified sweat-glands, the latter sebaceous glands, the ducts of 

 which usually open close to or into the mouths of the follicles of the eye-lashes. 



