360 HANDBOOK OF PHYSIOLOGY. 



ous lengths, among which, again, the deepest cells of the epithelium are 

 found spheroidal, irregularly oval, spindle-shaped or conical. 



The Urinary Bladder. The urinary bladder, which forms a re- 

 ceptacle for the temporary lodgment of the urine in the intervals of its 

 expulsion from the body, is more or less pyriform, its widest part, which 

 is situate above and behind, being termed the fundus: and the narrow 

 constricted portion in front and below, by which it becomes continuous 

 with the urethra, being called its cervix or neck. 



Structure. It is constructed of four principal coats serous, mus- 

 cular, areolar or submucous, and mucous. (a) The serous coat, which 

 covers only the posterior and upper half of the bladder, has the same 

 structure as that of the peritoneum, with which it is continuous, (b) The 

 fibres of the muscular coat, which are unstriped, are arranged in three 

 principal layers, of which the external and internal have a general lon- 

 gitudinal, and the middle layer a circular direction. The latter are es- 



FIG. 250. Epithelium of the bladder; a, one of the cells of the first row; 6, a cell of the second 

 row; c, cells in situ, of first, second, and deepest layers. (Obersteiner.) 



pecially developed around the cervix of the organ, and are described as 

 forming a sphincter vesicce. The muscular fibres of the bladder, like 

 those of the stomach, are arranged not in simple circles, but in figure- 

 of-8 loops, (c) The areolar or submucous coat is constructed of con- 

 nective tissue with a large proportion of elastic fibres, (d) The mucous 

 membrane, which is rugose in the contracted state of the organ, does not 

 differ in essential structure from mucous membranes in general. Its 

 epithelium is stratified and closely resembles that of the pelvis of the 

 kidney and the ureter (Fig. 250). 



The mucous membrane is provided with mucous glands, which are 

 more numerous near the neck of the bladder. 



The bladder is well provided with Hood- and lymph-vessels, and with 

 nerves. The latter are branches from the sacral plexus (spinal) and 

 hypogastric plexus (sympathetic). A few ganglion-cells are found, here 

 and there, in the course of the nerve-fibres. 



