EPITHELIUM 33 



two thio - amino - propionic acid molecules linked to- 

 gether. 



H NH, 



I I " 

 H— C— C— CO.OH 



I I 

 S H 



I 



S H 



I I 

 H—C—C— CO.OH 



I I 

 H NH, 



Tyrosin (p. 17) is also relatively abundant. 

 (c) Transitional Epithelium. — A slightly modified stratified 

 squamous epithelium lines the urinary passages. It is char- 



a h 



Fig. 6. — (a) Columnar Epithelium from the small intestine ; {b) Ciliated 

 Epithelium from the trachea. 



acterised by the more columnar or pear-like shape of the cells 

 of the deeper layers, and by the cells being very elastic, so that 

 they may be stretched or compressed according to the state 

 of the viscus they line. 



lining 



2. Columnar Epithelium (fig. 6, a). — The cells 

 the stomach and intestine in the embryo elongate at right 

 angles to their plane of attachment, and become columnar' 

 in shape. The free border of the cells has an appearance 

 like a hem, due to a series of short rods placed side by side. 

 The great function of this form of epithelium is to absorb 

 the digested matter from the intestine, and to pass it 

 on to the blood. 

 3 



