S3 6 THE URINARY APPARATUS. [OH. xxxvi. 



arches, parallel to, but more complete than the corresponding 

 arterial arches ; they ultimately unite to form the renal vein that 

 leaves the hilus. These veins receive also others which have a 

 stellate arrangement near the capsule (vence stellulce). 



The medulla is supplied by pencils of fine straight arterioles 

 which arise from the arterial arches. They are called arteriae 

 rectce. The efferent vessels of the glomeruli nearest the medulla 

 may also break up into similar vessels which are called false 

 arteries rectce. The veins (venae rectce) take a similar course and 

 empty themselves into the venous arches. In the boundary zone 

 groups of vasa recta alternate with groups of tubules, and give 

 a striated appearance to this portion of the medulla. 



The Ureters. The duct of each kidney, or ureter, is a tube 

 about the size of a goose-quill, and from twelve to sixteen inches 

 in length, which, continuous above with the pelvis, ends below 

 by perforating 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 composed of areolar tissue lined by transitional epithelium. 



The Urinary Bladder, which forms a receptacle for the 

 temporary lodgment of the urine in the intervals of its expulsion 

 from the body, 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 continuous 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. 

 (6.) The fibres of the muscular coat, which are uustriped, are 

 arranged in three layers, of which the external 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 vesicae. (c.) The areolar or submucous coat 

 is constructed of connective-tissue with a large portion of elastic 

 fibres, (c?.) 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. 



