570 THE URINARY APPARATUS [CH. XXXVIII. 



The medulla is supplied by pencils of fine straight arterioles 

 which arise from the arterial arches. They are called arterice rectce. 

 The efferent vessels of the glomeruli nearest the medulla may 

 also break up into similar vessels which are called false arterice 

 rectce. The veins (pence rectce) take a similar course and empty them- 

 selves into the venous arches. In the boundary zone groups of vasa 

 recta alternate with groups of tubules, and give it a striated 

 appearance. 



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

 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; 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 is pyriform; its widest part, which is 

 situate above and behind, is termed the fundus ; and the narrow 

 constricted portion, 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. The circular muscular fibres are especially 

 developed around the cervix of the organ and form the sphincter 

 vesicce. 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 

 hypogastric 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 the epithelium is stratified like the epidermis, with which it 

 becomes continuous. The female urethra has stratified epithelium 

 throughout. The epithelium rests on a vascular corium, and this is 

 severed by submucous tissue containing an inner longitudinal and 

 an outer circular muscular layer. Outside this a plexus of veins 

 passes insensibly into the surrounding erectile tissue. 



Into the urethra open a number of oblique recesses or lacunce, a 

 number of small mucous glands (glands of Littre"), two compound 

 racemose glands (Cowper's glands), the glands of the prostate, and 

 the vas deferens. The prostate, which surrounds the commencement 

 of the male urethra, is a muscular and glandular mass. Its glands 



