URINARY BLADDER AND URETHRA. 433 



passes through it, are compressed, so that the edges of the slit-like opening of the 

 ureter are rendered more tense, and are thus approximated towards each other 

 (fig. 291). 



279. URINARY BLADDER AND URETHRA. Structure. The mucous membrane of the 

 bladder resembles that of the ureter ; the upper layers of the stratified transitional epithelium 

 are flattened. It is obvious that the form of the cells must vary with the state of distention or 

 contraction of the bladder. [The mucous membrane and muscular coats are thicker than in 

 the ureter. There are mucous glands in the mucous membrane, especially near the neck of the 

 bladder. ] 



Sub-mucous Coat. There is a layer of delicate fibrillar connective-tissue mixed with elastic 

 fibres between the mucous and muscular layers. 



[The serous coat is continuous with, and has the same structure as the peritoneum, and it 

 covers only the posterior and upper half of the organ.] 



Musculature. The non-striped, muscular fibres are arranged in bundles in several layers, an 

 external longitudinal layer, best developed on the anterior and posterior surfaces, and an inner 

 circular layer. [Between these two is an oblique layer. ] There are other bundles of muscular 

 fibres arranged in different directions. Physiologically, the musculature of the bladder represents 

 a single or common hollow muscle, whose function when it contracts is to diminish uniformly 

 the size of the bladder, and thus to expel its contents ( 306). 



The blood-vessels resemble those of the ureter. The nerves form a plexus, and are placed 

 partly in the mucous membrane and partly in the muscular coat, and, like all the extra-renal 

 parts of the urinary apparatus, are provided with ganglia, lying in the mucosa, sub-mucosa, 

 and connected to each other by fibres (Maier). Ganglia occur in the course of the motor nerve- 

 fibres in the bladder ( W. Wolff). Their functions are motor, sensory, excito-motor, and vaso- 

 motor. [Sympathetic nerve-ganglia also exist underneath the serous coat (F. Darivin).] 



A too minute dissection of the several layers and bundles of the musculature of the bladder 

 has given rise to erroneous inferences. Thus, we speak of a detrusor urinae, which, however, 

 consists chiefly of fibres running on the anterior and posterior surfaces, from the vertex to the 

 fundus. There does not seem to be a special sphincter vesical internus ; it is merely a thicker 

 circular (6 to 12 mm.) layer of non-striped muscle which surrounds the beginning of the 

 urethra, and which, from its shape, helps to form the funnel-like exit of the bladder. Numerous 

 muscular bundles, connected partly with the longitudinal and partly with the circular fibres of 

 the bladder, exist, especially in the trigone, between the orifice of the ureters. 



In the female, the urethra serves merely for the passage of urine. The mucous membrane 

 consists of connective-tissue with many elastic fibres, and provided with papilla?. It is covered 

 by stratified epithelium and contains several mucous glands (Littre). Outside this is a layer 

 of longitudinal, smooth, muscular fibres, and outside this again a layer of circular fibres. Many 

 elastic fibres exist in all the layers, which are traversed by numerous wide venous channels. 



The proper sphincter urethrae is a transversely striped muscle subject to the will, 

 and consists of completely circular fibres which extend downwards as far as the 

 middle of the urethra, and partly of longitudinal fibres, which extend only on the 

 posterior surface towards the base of the bladder, where they become lost between 

 the fibres of the circular layer. 



In the male urethra, the epithelium of the prostatic part is the same as that in the bladder ; 

 in the membranous portion it is stratified, and in the cavernous part the simple cylindrical form. 

 The mucous membrane, under the epithelium itself, is beset with papillce, chiefly in the 

 posterior part of the urethra, and contains the mucous glands of Littre. 



Non-striped muscle occurs in the prostatic part arranged longitudinally, chiefly at the 

 colliculus seminalis ; in the membranous portion the direction of the fibres is chiefly circular, 

 with a few longitudinal fibres intercalated ; the cavernous part has a few circular fibres 

 posteriorly, but anteriorly the muscular fibres are single and placed obliquely and longitudi- 

 nally. 



Closure of the Bladder. The so-called internal vesical sphincter of the 

 anatomists, which consists of non-striped muscle, is in reality an integral part of 

 the muscular coat of the bladder and surrounds the orifice of the urethra as far 

 down as the prostatic portion, just above the colliculus seminalis. It is, however, 

 not the sphincter muscle. The proper sphincter urethrae (sph. vesicae externus) 

 lies below the latter. It is a completely circular muscle disposed around the 

 urethra, close above the entrance of the urethra into the septum urogenitale at the 

 apex of the prostate, where it exchanges fibres with the deep transverse muscle of 

 the perinseum which lies under it. 



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