576 URINARY APPARATUS. 



Thus the peritoneum, after covering the walls of the pelvis, is reflected on the 

 organs contained in that cavity, and in particular on the bladder, around which 

 it forms an orbicular fold. This again gives rise to three secondary folds — a kind 

 of serous layers — which are usually termed the ligaments of the Madder. One of 

 these layers is single and vertical {broad ligament), and is fixed to the inferior 

 part of the fundus ; it is not rare to see it prolonged forward on the lower wall of 

 the abdomen, as far as the umbilicus ; on its free border it is said to have a thin 

 hem or cord — the last vestige of the urachus. If this cord exists — which appears 

 doubtful to us— it cannot possess the signification given to it ; for the urachus has 

 not, like the umbilical arteries, an abdominal portion ; it only commences at the 

 umbilicus to be prolonged in the cord to the allantois. The other two serous 

 layers {umbilical ligaments) — pairs and horizontal — are attached to the sides of the 

 fundus, and present, on their free border, a thick cord, the obliterated umbilical 

 artery. 



(These are the so-called /aZse ligaments. There are t7-iw ligaments, formed by 

 processes of the pelvic fascia, which, in the male, are : the inferior, attaching the 

 prostate gland to the bladder ; the lateral, attached to the sides ; and a recto- 

 vesical, between the bladder and rectum. In the female, there are the vesico- 

 uterine and recto-uterine ligaments.) 



Owing to this disposition of the peritoneum, the bladder is divided into two 

 perfectly distinct regions : an anterior, enveloped by a serous layer ; the other, 

 posterior, is brought in contact with the surrounding organs through the medium 

 of the loose and abundant connective tissue of the pelvic region. This tissue — 

 constantly mixed with adipose masses around the neck of the bladder — submits, 

 with the serous membrane of the anterior region, to the changes in form and 

 continual displacements of the urinary sac. 



Interior. — This pouch, studied internally, exhibits folds and ridges more or 

 less marked, according to its state of plenitude. It also shows, posteriorly, the 

 opening of the neck, which communicates with the urethral canal, and a little 

 higher, the orifices of the ureters. These three apertures circumscribe a smooth 

 triangular space — the trigone {trigonum vesicce). 



Structure. — The structure of the bladder is very simple. Two membranes 

 compose its walls, the internal of which is mucous, and the external muscular. 

 Anteriorly, the latter is covered by the peritoneum described above. 



The murous membrane is pale and thin, and is continuous with that lining 

 the ui'eter.s and the urethra. It shows some papillae and some simple tubular 

 glands towards the neck. Its epithelium is stratified and tesselated, the super- 

 ficial cells being very irregular. 



The muscular lager is composed of white fibres, the arrangement of which is 

 very complicated. Certain authorities describe three superposed planes, the fibres 

 of which pass in different directions. In the Horse, in which the walls of the 

 bladder are very tliin, these planes are dilhcult to demonstrate. The fibres are 

 longitudinal, circular, oblique, spiral, and even twisted towards the fundus of the 

 bladder ; the deep fibres are reticulated. In the posterior region they do not 

 form a sphincter around the neck of the organ, as is generally believed ; the real 

 sphincter is Wilson's muscle, which encircles the membranous portion of the 

 urethral canal. 



(A submucous lager, composed of vascularized connective tissue, has been 

 described ; it loosely connects the mucous and muscular layei"s.) 



Vessels and nerves. — The parietes of the bladder receive their blood from 



