536 MANUAL OF HISTOLOGY. 



merit of parts below, a return of the urine from the bladder into the ureters 

 is just as difficult as from the latter into the papillae. 



276. 



The urinary passages commence in the calyces renales at the pelvis of 

 the organ. In these parts we find an external fibrous tunic, a middle 

 layer of smooth muscular fibres crossing each other in various directions, 

 and but slightly developed in the calyces, and then an internal mucous 

 membrane with a smooth surface and laminated epithelium of peculiar 

 flattened cells, to which we have already referred (p. 141). Here we also 

 meet with either tubular or racemose mucous glands in man and the 

 larger mammals. They are not so frequently seen in man as in other 

 animals, as, for instance, in the horse. 



The ureter presents the same structure, except that its muscular tunic 

 is stronger, consisting of an external longitudinal and internal circular 

 layer of fibres, to which is added, lower down, a third and most internal 

 layer of longitudinal elements. Under the epithelial lining the blood- 

 vessels are arranged in a dense network of delicate tubes. In the fibrous 

 covering of the ureter in the rabbit a nervous p]exus, almost destitute of 

 ganglion cells, is to be found. The mode of termination of the nerves 

 is not yet known. 



As is well known, the ureters terminate in a round diverticulum known as 

 the bladder or vesica urinaria, piercing its walls obliquely. The structure 

 of the bladder is similar to that of the ureters. Its external surface is in 

 part covered by a serous membrane, the peritoneum. Its muscular coats, 

 however, attain a much greater degree of strength here than in the ureter, 

 and are no longer arranged with the same regularity, consisting for the 

 most part of obliquely running muscular bundles, interlacing in a retiform 

 manner. At the neck of the organ these fibres are disposed in a thick 

 circular fasciculus, the sphincter vesicce, besides which they form, externally, 

 on the anterior wall and summit, longitudinal masses, to which the term 

 detrusor urinw is applied. However, much variety is to be observed in the 

 arrangement of the muscular tissue. Within the organ the mucous mem- 

 brane presents a smooth surface and characteristic flattened epithelium. 

 A few scattered mucous glands of small size may be found in the fundus and 

 around the neck. Here also a complicated network of capillaries lies close 

 under the epithelium. The manner in which the nerves of the bladder ter- 

 minate is just as obscure as in the ureters. 



The female urethra is lined by a mucous membrane thrown into heavy 

 longitudinal folds and covered with papillae. It is studded also, in the 

 neighbourhood of the bladder, with a number of mucous glands of either 

 simple or complex structure, the largest of which are known by the name 

 of glands of Littre. The muscular substance of the part, which is of con- 

 siderable thickness, consists of separate longitudinal and oblique bundles 

 of fibres ; the epithelium is of the flattened species. The vascularity of the 

 walls is very considerable, the vessels having a plexiform arrangement. 



5. The Generative Apparatus. 



277. 



The generative apparatus of the female consists of the ovaries, the 

 Fallopian tubes, opening into a diverticulum called the uterm, the vagina, 

 and external genital organs. Finally, the mammary gland is connected 

 with the reproductive functions of the female. 



