Alt — Glandular Structures Appertaining to the Human Eye. 191 



never quite reach the upper (in the lower eyelids the lower) 

 edge of the tarsus. The acini begin somewhat removed from 

 the external orifice of this central duct and sit upon it very 

 much like grapes on the central stem. They form usually 

 four rows around it, one on the posterior and one on its 

 anterior surface, one on its nasal and one on its temporal side 

 (Figs. 27, 28). The external orifices of the excretory ducts 

 lie side by side at the free edge of the lid behind the lashes. 

 The dermal epithelium reaches inwards into these ducts for 

 some distance, as is particularly well shown in the eyelids of 

 the Negro (Fig. 26). 



The acini of these glands as well as their ducts are lined 

 with several layers of flat polygonal epithelial cells. These 

 continually undergo a fatty degeneration and thus form a 

 sebaceous secretion which renders the lidmargins fatty and 

 thus helps to retain the tear-fluid within the conjunctival 

 sac. In their structure these glands differ in no way 

 from the sebaceous glands of the skin ; they differ only in 

 size. 



The length of the individual Meibomian glands varies ac- 

 cording to the height of the tarsal tissue. Thus, the longest 

 ones lie in the middle line of the eyelid, and from there they 

 grow gradually shorter towards both canthi. The most 

 nasally or temporally situated ones often consist only of the 

 central duct and two or three acini. 



I can find only one layer of Meibomian glands, and all 

 statements, referring to two or even more layers, are un- 

 doubtedly due to oblique sections. In a general way these 

 glands run parallel to each other and at right angles to the 

 lidmargin. Yet, deviations from this rule are not uncommon 

 (Fig. 28). 



The second kind of glands, the acino-tubular ones (Wald- 

 eyer), are usually drawn and described as lying solely in the 

 temporal part of the tarsus above (in the lower lid below) the 

 Meibomian glands (Fig. 29 to 31). This seems to be their 

 most frequent location, or at least, they seem to be generally 

 best developed in this portion of the tarsus. They are how- 

 ever, at least in the upper eyelid, quite frequently found to 

 be located, also, near and in the middle line (Figs. 23 to 25), 



