424 THE SKIN AND THE SENSE-ORGANS. 



fine twigs to the walls of the vessels (Fig. 261 I). He dis- 

 tinguishes three kinds of pigmented cells. 



b.-. The Harderian gland is situated at the inner angle of the 

 eye, and is pear-shaped in form. It consists of a number of 

 racemose glands held together by connective-tissue, the whole being 

 enclosed in a relatively thick and strong capsule of connective- 

 tissue. 



The alveoli have a diameter of O'O4O-o*o6o mm. : they possess a 

 lining of epithelium and a lumen which varies considerably in size. 

 The epithelial layer is bounded externally by a membrana propria. 

 The cells are placed eccentrically, they are cylindrical, and com- 

 posed of finely granular protoplasm ; each cell contains a pale, 

 rounded nucleus. The ducts of the alveoli are lined with a 

 single layer of cylindrical epithelium, the cells of which are usually 

 shorter and narrower than those of the epithelium of the alveoli ; 

 the ducts open into a single main tube, lined with similar epithelium 

 but strengthened externally by a layer of connective-tissue. The 

 glands secrete a fluid which moistens the free surface of the eye. 



The Harderian glands are surrounded by a rich capillary anasto- 

 mosis which completely invests the alveoli. 



c. The lachrymal duct opens behind and below into the nasal 

 cavity (see p. 389), anteriorly it can be traced forwards, as a small 

 tube imbedded in connective-tissue and lying immediately beneath 

 the skin, to the outer angle of the eye, where it opens by numerous 

 tubules. 



The lachrymal duct is lined with ciliated columnar epithelium. 



