THE LACHRYMAL GLAND l69 



thickness. The inner portion is very celluhir containing numer- 

 ous lyniplioid cells, while the outer boundary is more or less fibrous. 

 This outei" bomidary is immediately surrounded by the general 

 connective tissue of the palpebral fascia. Sections stained by 

 Van Gieson's method show the presence of numerous small ves- 

 sels accompanying the duct. Smooth muscle cells are also seen 

 in this connective tissue coat. They occur as a rule singly and 

 do not constitute a coat. Collagenous fibres greatly predominate. 



Weigert's stain shows the presence of numerous interlacing 

 elastic tissue fibres which form a more or less indefinite layer 

 outside of the basement membrane. 



Primary ducts. These ducts represent the first branches of the 

 main duct and are very irregular in size. As a rule the lumina 

 are round or oval and have an average diameter of 0.2 mm. 

 The primary ducts are embedded and surrounded by a large 

 amount of connective tissue which is derived from the septa. 

 The epithelial wall averages 20ju in thickness and is as a rule 

 made up of several layers of cells — varying from two to three 

 layers, the former predominating. In many instances, however, 

 a single layer of long columnar cells forms the entire epithelial 

 wall. Where two layers are present there is an interdigitation 

 seen between the long columnar cells and the basal more or less 

 irregularly cuboidal cells. 



The cytoplasm of the surface layer in the usual fixatives stains 

 homogeneously. The nuclei are either oval or round and have 

 an average diameter of from 7 to 10^. Clumps of chromatin 

 irregularly distributed are readily made out within the nuclei. 

 In many stains a definite cell boundary cannot be made out. 

 However, it is plainly seen in thin sections and especially after 

 the use of iron haematoxylin. 



The cells of the outer layer, or layers, are irregularly cuboidal 

 in form. The nuclei and cytoplasm show the same staining 

 characteristics as the inner layer. The nuclei of the outer layer 

 are frequently so arranged that their long axes are parallel to 

 the circumference of the duct, while those of the inner layer are 

 ]-adially arranged to the duct. This condition, however, is 

 much more pronounced in the smaller ducts. 



