CII. XXXVI.] 



THE BLADDER AND URETHRA 



541 



length, which, continuous above with the pelvis, ends below by per- 

 forating obliquely the walls of the bladder, and opening on its 

 internal surface. 



It is constructed of three coats : (a) an outer fibrous coat ; (b) a 

 middle muscular coat, of which the fibres are unstriped, and arranged 

 in three layers the fibres of the central layer being circular, and 

 those of the other two longitudinal in direction; the outermost 

 longitudinal layer is, however, present only in the lower part of 

 the ureter; and (c) a mucous membrane continuous with that of 

 the pelvis above, and of the urinary bladder below. It is com- 

 posed of areolar tissue lined by transitional 

 epithelium. 



The Urinary Bladder, which forms a 

 receptacle for the temporary lodgment of the 

 urine, is pyriform ; its widest part, which is 

 situate above and behind, is termed the 

 fundus; and the narrow constricted portion 

 in front and below, by which it becomes con- 

 tinuous with the urethra, is called its cervix 

 or neck. 



It is constructed of four coats, serous, 

 muscular, areolar or submucous, and mucous, 

 (a) The serous coat, which covers only the 

 posterior and upper part of the bladder, has 

 the same structure as the peritoneum, with 

 which it is continuous, (b) The fibres of the 

 muscular coat, which are unstriped, are 

 arranged in three layers, of which the exter- 

 nal and internal have a general longitudinal, 

 and the middle layer a circular direction. 

 The latter are especially developed around 

 the cervix of the organ and form the sphincter 

 vesicce. (c) The areolar or submucous coat is constructed of con- 

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

 membrane is like that of the ureters. It is provided with mucous 

 glands, which are most numerous near the neck of the bladder. 



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

 with nerves. The latter consist of branches from the sacral and hypo- 

 gastric plexuses. Ganglion cells are found, here and there, on the 

 course of the nerve-fibres. 



The Urethra. This occupies the centre of the corpus spongiosum 

 in the male. As it passes through the prostate it is lined by transi- 

 tional, but elsewhere by columnar epithelium, except near the orifice, 

 where it is stratified like the epidermis with which it becomes con- 

 tinuous. The female urethra has stratified epithelium throughout. 



FIG. 420. Diagram showing the 

 relation of the Malpighian 

 body to the uriniferous ducts 

 and blood-vessels, a, one of 

 the interlobular arteries ; a', 

 afferent artery passing into 

 the glomerulus ; c, capsule of 

 the Malpighiau body, form- 

 ing the commencement of and 

 continuous with t, the urini- 

 ferous tube ; e', e', efferent 

 vessels which subdivide and 

 form a plexus, p, surround- 

 ing the tube, and finally 

 terminate in the branch of 

 the renal vein e. (After Bow- 

 man.) 



