THE URINARY ORGANS. 167 



mcatus the mucous membranes are capable of secreting mucus, which 

 is much increased in amount under the influence of irritating sub- 

 stances, such as concentrated urine or the various causes of inflam- 

 mation. The bloodvessels are most numerous and of largest size 

 in the areolar tissue beneath the epithelium, and are accompanied 

 by the lymphatics. The nerves are distributed chiefly to the mus- 

 cular coats, but also extend into the fibrous tissue, up to and into 

 the epithelium. The cells of the latter are connected by little 

 protoplasmic bridges, as in the case of the epidermis, leaving minute 

 channels between the cells for the passage of nutrient fluids. 



