866 A MANUAL OF ANATOMY 



arranged in a coarsely reticular manner, a condition known as the 

 fasciculated bladder. 



The submucous coat is situated between the muscular and 

 mucous coats, which it connects in a loose manner for the most 

 part, and it is composed of areolar tissue with an admixture of 

 elastic tissue. It serves as a bed in which the arteries and nerves 

 subdivide before entering the mucous coat. 



The mucous coat is soft in consistence, and of a pinkish colour in 

 health. It is continuous with the mucous membrane of the ureters 

 and urethra, and over the greater part of the empty bladder is 

 thrown into folds, which, however, disappear as the viscus becomes 

 distended. This rugose condition is explained by the loose con- 

 nection which exists between the mucous and muscular coats 

 through means of the submucous coat. Over the internal trigone, 

 however, to be presently described, the mucous membrane is quite 

 smooth, and also very sensitive. The mucous coat is covered by 

 stratified transitional epithelium, similar to that of the ureters. 

 In the most superficial layer the cells are cubical, and they present 

 depressions on their deep surfaces, which receive the round ends 

 of the pyriform cells of the layer beneath. In the second layer the 

 cells are pyriform, the round ends being capped by the cubical cells of 

 the first layer, and the narrow ends being deeply placed amongst the 

 deeper cells. In the third and fourth layers the cells are round or oval. 



Orifices of the Bladder. — These are three in number, namely, 

 urethral, and two ureteric. The urethral orifice is the opening by 

 which the urine leaves the bladder, and it is situated at the posterior 

 extremity of the inferior surface, where it meets the base. This 

 is the most dependent part of the viscus, and corresponds with 

 the neck, which is surrounded by the base of the prostate gland. 

 Immediately above the urethral orifice the mucous membrane 

 presents a short median vertical ridge, which projects forwards 

 over the orifice. This ridge is called the uvula vesicce. It is pro- 

 duced by the middle lobe of the prostate gland, and is much more 

 conspicuous when that lobe is enlarged. The ureteric openings 

 assume the form of small slit-like, somewhat elliptical, apertures, 

 which are about ij inches apart, and an equal distance from the 

 urethral orifice, their direction being obliquely downwards and 

 inwards. The ureters, before so terminating, have pierced the 

 vesical wall obliquely, lying in it for about | inch, and in this 

 manner reflux of urine is prevented. 



Internal Trigone of the Bladder.— This is situated at the lower 

 part of the basal surface, and the mucous membrane over it is so 

 closely connected to the muscular coat that it is always smooth, 

 and so presents a marked contrast to the rugose condition of the 

 mucous membrane over the rest of the empty bladder. The 

 trigone assumes the form of an equilateral triangle, the angles of 

 which correspond with the urethral and ureteric openings, whilst 

 the sides are constructed by ridges connecting these openings. 

 The inter-ureteric ridge, called Merciers bar, is produced by a 



