////-. nir.rni; i. ::; 



lull i-iof. This pouch, studied internally, exhibit^ folds and riders more 

 MI- less marked, according to its state of plenitude. It also shews, ]>">- 

 teriorly, the opening of the neck, which communicates with the urethral 

 canal, and a little higher, the orifices of tho ureters. These throe apertures 

 cin -u inscribe a triangular space, the trigonum vesicse. 



STBUCTURE. The structure of the bladder is very simple. Two mem- 

 branes compose its walls, the internal of which is mucous, and tho external 

 muscular. Anteriorly, tho latter is covered by the serous investment 

 described above. 



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

 tho ureters and the urethra. It shows some papillae and some simple 

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

 the superficial cells being very irregular. 



The mum-nidi- layer is composed of white fibres, the arrangement of which 

 is very complicated. Certain authorities describe three superposed planes, 

 whose fibres pass in different directions. In the Horse, the walls of whoso 

 bladder are very thin, these planes are difficult 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. 



Vessels and nerves. The parietcs of the bladder receive their blood 

 from several sources. Tho principal arteries come from tho vesico-prostatic 

 branch of the internal pudic ; the umbilical artery also furnishes ramifications 

 that reach the fundus of the organ. The lymphatics pass to the sublumbar 

 glands. The nerves are furnished by the pelvic or hypogastric plexus, and 

 the inferior branches of the two last sacral pairs ; their twigs are spread 

 more especially between the muscular and mucous layers. 



DEVELOPMENT. The study of the development of the urinary reservoir 

 is very interesting. It is narrower and more elongated in the foetus than 

 tho adult, and is relatively more capacious during the whole period of intra- 

 uterine life. It then occupies the abdominal cavity as far as the umbilical 

 upeiiing, and is flanked by the two umbilical arteries. Its posterior 

 extremity alone enters the pelvis ; the anterior extremity, forming a veritable 

 neck, is continuous with the urachus, just as the neck, properly so called, is 

 continuous with the urethral canal (Fig. 253). At birth, this anterior neck 

 separates from the nraehus, and is transformed into a five cnl-<l<--Km- ; \\hile 

 the bladder is gradually withdrawn into tho pelvic cavity, carrying with it 

 the umbilical arteries, and finishes by acquiring tho position it definitively 

 preserves in the adult. 



FUNCTIONS. The part played by tho bladder is one of iurontesf bl.- 

 utility. In permitting the accumulation of tho urine and the intermittent 

 expulsion of that excremcntikial fluid, it spares animals the disajn . !.!< 

 condition in which they would bo placed if the liquid secreted by the 

 kidneys was continually being discharged as it was produ 



4. 1'i-rtitrn. 



Tho description of this organ will bo given with that of tho 

 .s ; as in the malt; it is common to the urinary and generative a 

 mile it is intimately connected with the latter. 



