376 HISTOLOGY OF THE MORBID PROCESSES. 



be transverse to the direction of the tube. In glandular tubules the 

 epithelial cells are usually well-defined and clearly distinguishable 

 from each other. This is not apt to be the case in immature endo- 

 thelium. 



2. Lymphangioma. What has already been said with respect to 

 the hsemangiomata applies to the lymphangiomata. Many of these 

 tumors appear to be the result of a dilatation of the lymphatic 

 vessels normally present in the tissues; but cases may arise in 

 which there is a real reproduction of those vessels. The spaces in 

 the tumor are either empty and collapsed, or they contain lymph 

 and not blood. The walls of the vessels are frequently thickened 

 by the production of fibrous tissue around them. 



IV. THE EPITHELIAL TUMORS. 



The epithelium, which by its proliferation gives rise to tumors, 

 may be situated either within a glandular structure of the body or 

 upon one of its free surfaces, such as the skin or a mucous mem- 

 brane. The tumors which result are not wholly composed of epithe- 

 lium. There is always a development of the connective tissue of 

 the part, furnishing a vascularized nutrient substratum for the 

 epithelium. The epithelium of glandular organs may give rise 

 to two sorts of tumors, the adenomata and the carcinomata. The 

 stratified epithelium of the skin and some of the mucous membranes 

 proliferate to form the epitheliomata. 



1. Adenoma. In this form of epithelial tumor there is a more 

 or less perfect adherence to the structure of a normal gland. When 

 adenomata spring from the epithelium of tubular or acinous glands 

 the lobules of the tumor are composed of tubes or acini with a 

 distinct lining of epithelium enclosing their lumina (Fig. 340). But 

 there is almost always some departure from the typical structure 

 of a gland ; the lobules may be of unequal size in a more marked 

 degree than is usual, the character of the epithelial lining may be 

 abnormal, or the distribution and arrangement of the lobules may 

 betray an abnormal tendency on the part of the growth. The 

 latter feature is exemplified in the adenomata of the rectum, in 

 which the new-formed glandular structure is apt to penetrate the 

 muscularis mucosse and develop abundantly in the submucous coat 

 or even in the deeper, muscular tissues of that part of the in- 

 testine. 



