I9IO HUMAN ANATOMY. 



the vesical trigone, however, this layer becomes condensed and forms a compact 

 transverse muscular sheet that is closely united to the overlying mucous membrane 

 and, in conjunction with the muscular tissue of the urethra, surrounds the beginning 

 of that canal with a constrictor-like tract, the mteryial vesical sphincter. 



The outer fibrous coat of the vesical wall is strongest over the inferior surface, 

 where it receives reflections from the pelvic fascia; towards the apex and beneath the 

 peritoneum it is less definite and often intermingled with adipose tissue. Over the 

 postero-inferior surface in the male it is fused with the fibrous tissue surrounding the 

 seminal vesicles and ducts, and in the female is blended with the anterior vaginal wall. 



Vessels. — The arteries supplying the bladder are chiefly the superior and 

 inferior vesical, from the anterior division of the internal iliac ; these are reinforced 

 by branches from the middle hemorrhoidal, as well as by small twigs from the internal 

 pudic and the obturator arteries. The superior vesical supplies the upper segment 

 of the bladder and sends small branches along the urachus. The inferior vesical 

 divides into two or more branches which are distributed to the infero-lateral and 

 postero-inferior surfaces. In addition to twigs to the region of the trigone, others 

 pass to the prostate, seminal vesicles, and ducts. On gaining the bladder, the vesical 

 branches anastomose and enclose that organ in an arterial net-work from which 

 twigs enter the muscular coat and break up into capillaries for its supply. Others 

 penetrate the muscular tunic and within the submucosa form a net-work from which 

 arterioles pass inward for the supply of the mucous membrane. 



The vei7is do not accompany the arteries, but form a submucous plexus that 

 drains the mucous membrane and empties into a muscular plexus which, in turn, is 

 received by an external subperitoneal plexus. From the latter the blood from the 

 entire organ passes into the large prostatico-vesical plexus at the sides of the bladder 

 and thence into the tributaries of the internal iliac veins. With the exception of the 

 smaller ones on the inferior surface, all the vesical veins possess valves (Fenwick). 



The lymphatics of the bladder begin as a close-meshed net -work within the mus- 

 cular coat, according to Gerota,^ being absent within the mucous membrane. Out- 

 side the muscular coat they form a wide-meshed subperitoneal plexus, those from the 

 apex and body coursing downward and laterally and those from the fundus upward. 

 Leaving the sides of the bladder, the efferent channels, chiefly in company with the 

 arteries, pass to the internal iliac lymph-nodes and to those situated at the bifurca- 

 tion of the aorta. Along the path of the lymphatics on the antero-inferior surface of 

 the bladder Gerota describes one or two very small nodes as usually present. 



The nerves of the bladder include both sympathetic and spinal fibres. The 

 former, distributed chiefly to the muscular tissue, are from the vesical plexuses, which, 

 as subordinate divisions of the pelvic plexuses, lie at the sides of the bladder. 

 The sympathetic fibres accompany the arteries and are joined by the vesical branches 

 from the sacral plexus derived from the third and fourth, possibly also the second, 

 sacral spinal nerves. The principal trunks reach the bladder in the vicinity of the 

 ureters, the trigonal region receiving the most generous nerve-supply and the apical 

 segment the fewest fibres. Within the outer fibrous coat the larger nerves divide 

 into smaller branches that are connected with ganglia, especially in the neighborhood 

 of the ureters, from which twigs enter the muscular tunic and break up into smaller 

 ones bearing terminal microscopic ganglia before ending in the muscle. Other 

 branches penetrate the submucosa, where they form plexiform enlargements contain- 

 ing numerous minute ganglia, from which fine twigs proceed to the mucosa to end, 

 according to Retzius, between the epithelial cells. In general the sensibility of the 

 normal bladder is comparatively slight, the trigonal region, especially at the ureteral 

 openings, being its most sensitive area. 



PRACTICAL CONSIDERATIONS: THE BLADDER. 



Absence of the bladder is a very rare abnormality, but in more than one case 

 has proved to be consistent with prolonged life, the dilated ureters — opening into the 

 urethra — having acted as reservoirs for the urine and the muscle-fibres at their con- 

 stricted orifices having taken on sphincteric action and prevented urinary incon- 



^ Anatom. Anzeiger, Bd. xii., 1896. 



