CHAP. XVI:] ELIMINATION. 181 



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 in length, and three inches across, and the 

 ordinary amount of urine which it contains is about one pint. 

 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 cir- 

 cularly, the circular fibres being collected 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 nor- 

 mally 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 for- 

 wards. 



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

 about an inch and a half 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 direction 

 is obliquely downwards and forwards, its course being slightly 

 curved, the concavity directed forwards and upwards. It ad- 

 mits of considerable dilatation, its normal diameter, however, 

 being about a quarter of an inch. It is lined by a mucous coat, 

 which is continuous, externally, with that of the vulva, and, 

 internally, with that of the bladder. The external 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. 



