460 



PHYSIOLOGY 



CHAP. 



IX. The ureters open into the bladder by two oblique orifices 

 that function as valves, and close by the positive intravesical 

 pressure. While this impedes reflux into the ureters, the flow 

 of urine into the bladder, caused by the rhythmical peristaltic 

 movements of the ureters, which drives the fluid forward, and 

 opens the orifices, is not prevented. 



The Bladder has an external serous or peritoneal coat which 

 lines only the posterior and upper half, an internal mucous 

 membrane which is covered with stratified epithelium similar to 



FIG. 126. Course of the muscular fibres of the bladder (Allen Thomson after Pettigrew, and from 

 nature), . A. From the front. On the right side the superficial fibres are shown ; on the 

 left, the deep or circular fibres ; a, on the right side the median and most superficial bands of 

 the longitudinal fibres, showing slight decussation of the fibres ; a', those diverging somewhat; 

 a", the lowest, which pass much more obliquely ; the attachment of the longitudinal fibres to 

 the prostate is shown. On the left side, c the upper, d the middle, c", the lowest set of 

 circular or deeper fibres ; s, the thickest and most transverse sets of three fibres forming the 

 sphincter ; p, right half of the prostate, the left half having been removed ; u, urachus 

 into which some of the longitudinal fibres are prolonged. B. From the lad:. Right side 

 shows superficial fibres ; left, the deeper fibres of the same kind, or intermediate fibres ; and 

 some of the circular fibres ; b, b, median, most superficial and strongest bands of longitudinal 

 fibres on right side ; V, more diverging fibres near middle of bladder ; &', the most divergent 

 which surround entrance of ureters. On left side, c, c', and c" indicate the deeper circular fibres 

 passing round at various levels, and crossing with the deeper diverging fibres posteriorly ; s, 

 the most transverse fibres at the neck forming the sphincter ; u, the urachus ; ur, the ureters ; 

 the left half of the prostate has been removed to show the sphincter ; r, part of right vas 

 deferens and vesicula seminalis. 



that of the ureters, and an intermediate muscular coat, which calls 

 for special consideration. 



The muscular coat has >an outer layer, the fibres of which are 

 mainly longitudinal, and are most distinct upon the anterior and 

 posterior surfaces of the bladder, and an inner layer of which the 

 fibres are mostly circular, which is thinner and irregularly reticu- 

 lated (Fig. 126). This distinction into two or three layers is, 

 however, only an anatomical device, since the fibres of which they 



