THE GASTRO-INl^ESTINAL CANAL. 145 



structural elements: I. epithelial or gland-cells; 2. 

 a connective-tissue framework, with blood- and 

 lymphatic-vessels and nerves. The epithelial cells, 

 usually large, differ in form in different and even in 

 the same glands : in the latter case especially, when 

 the gland is divided into a secreting and excretory 

 portion. They will be described when we study the 

 glands in detail. The connective tissue, varying 

 greatly in amount in different glands, is sometimes 

 arranged in sheets and bundles so as to form 

 variously shaped cavities which are lined with the 

 gland-epithelium ; sometimes, in the form of simple 

 or superimposed lamellae covered with flat cells like 

 endothelium, it forms thin-walled tubes or chambers 

 on whose sides the cells are placed ; in this form it 

 is called the membrana propria of the gland cavities. 

 The cavities and tubes thus formed and lined with 

 gland-epithelium are variously arranged in different 

 glands, but their different modes of arrangement 

 may be reduced to three types : 



1. Tubular Glands , which have the form of simple 

 or occasionally branching, straight, curved, or vari- 

 ously contorted tubes, terminating in blind extremi- 

 ties. Such are the glands of the stomach. 



2. Racemose Glands, in which the secreting portion 

 in the form of vesicular or irregular-shaped cavities 

 alveoli are grouped around simple or branching 

 excretory ducts, into which they open ; the whole 



structure has been not inaptly compared to a bunch 

 10 



