THE URINARY BLADDER. - 127 



which is a membranous cylindrical tube, rather flattened, and 

 between three and five lines in diameter, with some variations 

 in this respect. 



The Ureters descend from the pelvis of the kidney so as to 

 pass obliquely across the psoas muscle and the great iliac 

 vessels. They are behind the peritoneum, but in contact with 

 it. They approach the pelvis near the junction of the os ilium 

 with the sacrum, and thence descend forwards and inwards, 

 surrounded with loose cellular membrane, to the lower part of 

 the bladder into which they are inserted at its external and 

 posterior part. They first penetrate obliquely the muscular 

 coat, and then proceed between the muscular and internal 

 coats from half an inch to an inch, in an oblique direction, 

 from without inwards and forwards, when they terminate by 

 small orifices in the internal coat, each of which is at an equal 

 distance, (rather more than an inch,) from the orifice of the 

 uretha, thus forming a triangle with it. 



The ureters are said to have three coats. The exterior ap- 

 pears to be derived from the cellular substance ; within it is 

 another, which has been regarded very differently by different 

 anatomists ; some considering it as merely membranous, and 

 others as muscular. If the ureter be laid open and the internal 

 coat peeled off, the muscular structure of this coat is often very 

 perceptible. 



The internal coat is called villous, or mucous, and is continued 

 from the internal coat of the bladder. Over this coat mucus is 

 constantly spread, which defends it from the acrimony of the 

 urine. It is very difficult to separate the two last mentioned 

 coats from each other. 



The ureters receive blood-vessels and nerves from those of 

 the neighboring parts. Their internal coat is very vascular, 

 and is also very sensitive to irritation. The passage of a small 

 urinary calculus can be traced from the pelvis of the kidney 

 to the bladder, by the exquisite pain and the spasmodic affec- 

 tions which it often excites. 



Of the Urinary Bladder. 

 The urinary bladder is a large sac, of a muscular and mem- 



