204 ANATOMY FOE NUESES. [CHAP. XVII 



The bladder. The bladder is the reservoir of the urine. It 

 is situated in the pelvic cavity behind the pubes, and is held in 

 position by ligaments. During infancy it is conical in shape 

 and projects above the upper border of the pubes into the hypo- 

 gastric region. In the adult, when quite empty, it is placed 

 deeply in the pelvis ; when slightly distended, it has a round 

 form ; but when greatly distended, it is ovoid in shape and 

 rises to a considerable height in the abdominal cavity. (Vide 

 Plate VII.) When moderately distended, it measures about 

 five inches (127 mm.) in length, and three inches (76 mm.) 

 across, and the ordinary amount of urine which it contains is 

 about one pint (0.473 litre). The bladder consists of plain 

 muscular tissue lined by a strong mucous membrane, and is 

 covered partially by a serous coat derived from the peritoneum. 

 The muscular coat has three layers, the principal fibres of which 

 run longitudinally and circularly, the circular fibres being col- 

 lected into a layer of some thickness around the constricted 

 portion or neck, where the bladder becomes continuous with 

 the urethra. These circular fibres around the neck form a 

 sphincter muscle which is normally in a state of contraction, 

 only relaxing at intervals, when the accumulation of urine 

 within the bladder renders its expulsion necessary. 



The base of the bladder is directed downwards and back- 

 wards, and in the female lies in contact with the front wall of the 

 vagina and the lower part of the neck of the uterus. The neck 

 of the bladder is directed obliquely downwards and forwards. 



The urethra. The urethra is a narrow, membranous canal, 

 about an inch and a half (38 mm.) in length in the female, and 

 extending from the neck of the bladder to the external orifice 

 or meatus urinarius. It is placed beneath the symphysis pubis, 

 and is embedded in the anterior wall of the vagina. Its direc- 

 tion is obliquely downwards and forwards, its course being 

 slightly curved, the concavity directed forwards and upwards. 

 It admits of considerable dilatation, its normal diameter, how- 

 ever, being about a quarter of an inch (6.3 mm.). It is lined 

 by a mucous coat, which is continuous, externally, with that of 

 the vulva, and, internally, with that of the bladder. The exter- 

 nal muscular coat is also continuous with that of the bladder, 

 but between the mucous and muscular coats is a layer of thin, 

 spongy tissue, containing a network of large veins. 



