490 



Yertebrata. 



Pig^ etc.) the ovary, in 

 follicles, has a racemose 



The kidneys are short, roundish organs, with a large cavity, 

 the pelvis of thu kidney, into the inner side of which the urinary 

 tubules open ; several large papillse project into the pelvis from the 

 substance of the kidney (consisting of urinary tubules) surrounding 

 it; the pelvis is continued into the ureter. A urinary bladder is 

 present; for its opening and for that of the ureters, see the repro- 

 ductive organs. 



In most Mammalia the surface of the kidney is smooth; in others (e.r/,, Cattle) 

 lohed, in others again (Bear, Seal, Whales, etc.), the kidney is branched, and 

 consists of numerous lobules, each of which is mounted upon a branch of the 

 proximal end of the ureter, whilst they are only held together by loose connective 

 tissue. 



The ovaries are comparatively small, usually with a flat or 

 somewhat lobed surface ; in a few Mammals only (Monotremes, the 



consequence of the projecting Graaffian 

 appearance.* The Graaffian follicles as 

 described above, p. 351, differ from those 

 of other Vertebrata in that they are pro- 

 vided with a large number of follicle 

 cells, and contain a large cavity ; in 

 the Monotremes, however, just as in 

 the lower Vertebrates there is only one 

 layer of cells round the ovum, and 

 there is no cavity. Each oviduct in 

 the Mammalia in general is composed of 

 three regions ; an anterior, usually very 

 narrow, portion, the fallopian tube, 

 with a funnel opening into the abdominal 

 cavity; a median wider part, the uterus; 

 and a terminal section, the vagina; 

 in the Monotremes the division between 

 uterus and vagina is not demarcated, 

 and the oviducts open separately into 

 a saccular dilation of the ventral wall 

 of the cloaca, the urinogenital 

 sinus, into which the urinary bladder 

 of the two ureters also opens ; all five 

 apertures are close to its base. In the 

 Marsupials the cloaca is shortened, 

 so that it forms simply a shallow pit, 

 into which the rectum opens above, and the urinogenital sinus 

 below ; the two vaginse open separately on the floor of the urino- 



Fig. 399. The terminal portions 

 of the gut, of the urinary and 

 generative apparatus in the 

 females of various Mammalia 

 viewed from the side, diagram- 

 matic. A Monotreme, B Marsupial, 

 C other Mammalia, t bladder, cl 

 cloaca, e rectum, u uterus, ug urino- 

 genital duct, ul ureter, v vagina. — 

 Orig. 



* When the ovum leaves the foUiole the cavity is filled with very cellular connective 

 tissue, which in some Mammalia increases so much in size that the follicle becomes 

 many times as large as it was previously ; as large indeed as the whole of the rest of 

 the ovary. Later it degenerates to form the corpus Iviteum. 



