STRUCTURE OF URINARY BLADDER AND URETHRA. 519 



gages in increased activity for the propulsion of the urine, the portion of 

 the muscular fibers surrounding the pyramids so compresses the urinary 

 tubules that the urine cannot pass back into the excretory ducts of the 

 tubules. The return of urine from the bladder into the ureter is ren- 

 dered difficult in part by the fact that with marked stretching of the 

 bladder-wall the ureter, in so far as it is contained therein, is likewise com- 

 pressed ; and in part by the fact that the stretching of the mucous mem- 

 brane of the bladder firmly approximates the margins of the slit -like 

 openings of the ureters (Fig. 177). 



In case of retention of urine in the bladder, a return of urine into the ureters 

 may, it is true, take place. 



STRUCTURE OF THE URINARY BLADDER AND THE URETHRA. 



The mucous membrane of the bladder is not unlike that of the ureter. The 

 laminated epithelium exhibits flatter cells in the upper layer. When the bladder 

 is distended, the epithelial cells become stretched and thinner. The unstriated 

 muscular fibers are arranged in bundles that form an external longitudinal layer 

 and an internal circular layer. In addition, fibers pass in various directions and 

 cross one another, forming a wide-meshed trabecular network. Between the mus- 

 cular coat and the mucous membrane there is a layer of delicate, fibrillar, cellular 

 connective tissue, with an intermixture of elastic fibers. An excessively minute 

 dissection of the individual layers and bands of the musculature of the bladder 

 has given rise to erroneous physiological interpretations. In this category belongs 

 the establishment of a special detrusor urinas muscle, which is said to consist of 

 fibers pursuing a vertical direction from the vertex to the fundus, principally 

 upon the anterior and posterior surfaces. The conception of a special internal 

 sphincter vesicse is likewise unjustified as constituted of a circular layer of un- 

 striped muscles, from 6 to 12 mm. thick, surrounding the commencement of the 

 urethra, and in its form helping to give rise to the funnel-shape of the outlet of 

 the bladder. This layer, also designated annulus urethralis vesicae, is no sphincter 

 at all. In the trigone of Lieutaud there are, at times, between the orifices of 

 the ureters, numerous muscular bundles, attached in part to the circular, in part 

 to the longitudinal fibers of the wall of the bladder. Waldeyer believes, par- 

 ticularly of the trigone, that it facilitates the distention of the bladder, favors its 

 complete evacuation and aids its closure. 



From the physiological standpoint, it should be borne in mind that 

 the entire musculature of the bladder represents a continuous hollow 

 muscle whose sole function it is, in contracting, to diminish the cavity 

 of the bladder from all directions and to expel its contents. 



The vessels of the bladder resemble those of the ureter in their distribution. 

 The nerve-fibers are provided with ganglia, as is the case generally at all parts 

 of the urinary passages outside the kidney. These are situated in part in the 

 mucosa, in part in the muscularis, and they communicate with one another by 

 means of filaments. In the mucous membrane and its epithelium, the nerves 

 terminate in end-bulbs. In accordance with their functions, the nerves are motor, 

 sensory, reflex, and vascular. 



In women, the urethra serves only as the excretory duct of the urinary 

 bladder. The mucous membrane, formed of a large amount of fibrillary con- 

 nective and elastic tissue and supplied with papillae, is lined by laminated pavement 

 epithelium. In addition, a number of Littre's mucous glands are embedded in it. 

 Next to the mucous membrane is a layer of longitudinal unstriated muscular 

 fibers, and next to the latter a layer of circular fibers. These layers contain an 

 abundance of connective-tissue and elastic fibers, and, besides, extensive venous 

 plexuses, suggestive in their structure of cavernous spaces. 



The true sphincter muscle of the bladder is a striated muscle, which 

 undergoes contraction and relaxation under the influence of the will, and 

 consists in part of transverse, completely circular fibers, which extend 



