THE URETERS. 995 



or indirectly to form a dilated pouch, the pelvis, from which the ureter, after 

 passing through the hilum of the kidney, descends to the bladder. The calices are 

 cup-like tubes encircling the apices of the Malpighian pyramids ; but inasmuch as 

 one calyx may include two or even more papillae, their number is generally less 

 than the pyramids themselves, the former being from seven to thirteen, whilst the 

 latter vary from eight to eighteen. These calices converge into two or three 

 tubular divisions which by their junction form the pelvis or dilated portion of the 

 ureter. The portion last mentioned, where the pelvis merges into the ureter 

 proper, is found opposite the spinous process of the first lumbar vertebra, in which 

 situation it is accessible behind the peritoneum (see Fig. 507, page 924). 



The ureter proper is a cylindrical membranous tube, about sixteen inches in 

 length and of the diameter of a goosequill, extending from the pelvis of the kidney 

 to the bladder. Its course is obliquely downward and inward through the lumbar 

 region into the cavity of the pelvis where it passes downward, forward, and inward 

 across that cavity to the base of the bladder, into which it then opens by a con- 

 stricted orifice, after having passed obliquely for nearly an inch between its muscular 

 and mucous coats. 



Relations. In its course it rests upon the Psoas muscle, being covered by the 

 peritoneum, and crossed obliquely, from within outward, by the spermatic vessels ; 

 the right is crossed by the branches of the mesenteric arteries, which are distributed 

 to the ascending, and the left by those for the descending colon ; the right ureter 

 lying close to the outer side of the inferior vena cava. Opposite the first piece of 

 the sacrum it crosses either the common or external iliac artery, lying behind the 

 ileum on the right side and the sigmoid flexure of the colon on the left. In the 

 pelvis it enters the posterior false ligament of the bladder, below the obliterated 

 hypogastric artery, the vas deferens in the male passing between it and the bladder. 

 In the female the ureter passes along the side of the neck of the uterus and upper 

 part of the vagina. At the base of the bladder it is situated about two inches 

 from its fellow : lying, in the male, about an inch and a half from the vesical orifice 

 of -he urethra, at one of the posterior angles of the trigone. 



Structure. The ureter is composed of three coats a fibrous, muscular, and 

 mucous. 



The fibrous coat is the same throughout the entire length of the duct, being 

 continuous at one end with the capsule of the kidney at the floor of the sinus, while 

 at the other it is lost in the fibrous structure of the bladder. 



In the pelvis of the kidney the muscular coat consists of two layers, longitudinal 

 and circular: the longitudinal fibres become lost upon the sides of the papillae at 

 the extremities of the calices ; the circular fibres may be traced surrounding the 

 medullary structure in the same situation. In the ureter proper the muscular 

 fibres are very distinct, and are arranged in three layers an external longitudinal, 

 a middle circular, and an internal layer, less distinct than the other two, but 

 having a general longitudinal direction. According to Kb'lliker, this internal layer 

 is only found in the neighborhood of the bladder. 



The mucous coat is smooth, and presents a few longitudinal folds which 

 become effaced by distension. It is continuous with the mucous membrane of the 

 bladder below, whilst it is prolonged over the papillae of the kidney above. Its 

 epithelium is of a peculiar character, and resembles that found in the bladder. It 

 is known by the name of " transitional " epithelium. It consists of several layers 

 of cells, of which the innermost that is to say, the cells in contact with the 

 urine ai'e quadrilateral in shape, with a concave margin on their outer surface, 

 into which fits the rounded end of the cells of the second layer. These, the inter- 

 mediate cells, more or less resemble columnar epithelium, and are pear-shaped, 

 with a rounded internal extremity which fits into the concavity of the cells of the 

 first layer, and a narrow external extremity which is wedged in between the cells 

 of the third layer. The external or third layer consists of conical or oval cells 

 varying in number in different parts, and presenting processes which extend down 

 into the basement membrane. 



