1102 UROGENITAL SYSTEM. ™ 
muscle fibres which, near the urethral orifice, run circularly in a horizontal direction. 
These form a distinct layer over the base of the bladder and in the region of the urethral 
orifice, but elsewhere the bundles of fibres are separated from one another by considerable 
intervals, and are directed obliquely. The circular fibres in the region of the urethral 
orifice are sometimes described as forming a sphincter vesice. The inner stratum 
(stratum internum) is a thin layer of fibres directed for the most part longitudinally. 
The submucous coat (tela submucosa) is composed of areolar tissue, but contains 
numerous fine elastic fibres. 
The mucous coat (tunica mucosa) is loosely attached, through the submucous layer, to 
the subjacent muscular coat, except over the trigonum vesicxe. Over the trigonum it is 
always smooth and flat ; elsewhere it is thrown into folds when the organ is empty. The 
mucous membrane of the bladder is continuous with that of the ureters and urethra. The 
epithelium covering it varies much in appearance in different conditions of the organ, and 
is of the variety known as transitional stratified epithelium. 
Vessels and Nerves of the Bladder.—The bladder receives its blood supply on each side 
from the superior and inferior vesical arteries. The superior vesical artery arises from the 
pervious part of the hypogastric artery, and the inferior vesical from the internal iliac. The 
largest veins are found just above the prostate, and in the region where the ureter reaches the 
bladder. They form a dense plexus which pours its blood into tributaries of the internal iliac 
vein, and communicates below with the prostatic plexus. The lymphatics from the bladder join 
the iliac group of glands. 
The nerve supply of the bladder is derived on each side from the vesical plexus, the fibres of 
which come from two sources, namely (1) from the upper lumbar nerves through the hypogastric 
plexus, and (2) from the third and fourth sacral nerves. The fibres from the latter sources 
Join the vesical plexus directly. 
THE URETHRA. 
The urethra is the channel which serves to convey the urine from the bladder 
to the exterior. In the male it consists of two portions, a proximal part, less than 
one inch in length, extending from the bladder to the points where the ducts of 
the reproductive elands j oin the canal, and a much longer distal portion which 
Serves as a common passage for the secretion of the kidneys and for the generative 
products. An account of the male urethra follows the deseription of the male 
reproductive glands and passages (see p. 1119). In the female the urethra is more 
simple in its arrangement, and represents only the proximal part of the male 
urethra. It is a short passage leading from the bladder to the external urethral 
orifice—an aperture placed within the urogenital cleft immediately above and in 
front of the opening of the vagina. 
Female Urethra.—The female urethra (urethra muliebris) is a canal of one 
to one and a half inches in leneth, which follows a slightly curved direction down- 
wards and forwards, below and Tehind the lower border of the symphysis pubis. As 
it leaves the pelvis the urethra pierces the triangular ligament, and the part of the 
passage which hes between the deep and superficial layers of this hgament is sur- 
rounded by the fibres of the compressor urethree muscle. Except during the passage 
of fluid the canal is closed by the apposition of its anterior and posterior walls. 
The external orifice (orifictum urethre externum) is placed between the labia 
minora, immediately in front of the » opening of the vagina, and hes about one inch 
below and behind the clitoris (Fig. 778). The opening is slit-like, and is bounded by 
slightly marked lateral lips. The posterior wall of the urethra, except in its upper 
part, is intimately connected with the anterior wall of the vagina. The mucous 
lining of the canal is raised into a number of slightly marked longitudinal folds, one 
of which, more distinct than the others, and placed upon the posterior wall of the 
passage, receives the name of crista urethralis. 
Structure.—The muscular coat of the urethra (tunica muscularis) is continuous above 
with that of the bladder, and composed of layers of circularly and longitudinally disposed 
muscle fibres. Within the muscular coat the wall of the urethra is very V ascular, and the 
canal itself is lined by a pale mucous membrane which is thrown into longitudinally- 
directed folds, one of which is the crista urethralis mentioned above. The epithelium of 
the canal, in its upper part, is of the transitional variety, like that of the bladder; in its 
lower part, however, it becomes scaly. Numerous mucous glands (glandule urethrales) 
