332 THE UMNO-GENITAL SYSTEM, THE ADRENALS, ETC. 



testes (Fig. 214), that is, they are bilaterally symmetrical, and 

 placed on the ventral surfaces of the kidneys. 



The oviducts (Fig-. 224 Or) lie externally to the kidneys and 

 ovaries, and course through the whole length of the trunk from the 

 roots of the lungs to the cloaca. The size of the ovaries and oviducts 

 varies very greatly according to the season of the year ; at times, 

 the kidneys may be entirely hidden by them. 



I. THE URINAKY ORGANS. 

 A. The kidneys. 



a. General description. Each kidney (Fig. 215) is a reddish- 

 brown, elongated organ, almost semilunar in shape; the inner 



border being straight and the outer convex. 

 The organ is flattened from above down- 

 wards, and decreases in thickness towards 

 either end. In animals of average size 

 the kidney is about 16 mm. long, and 



The right kidney, seen from the ( . IT ml -, . -. 



ventral surface. irom 6 to 7 mm. broad. The kidneys 



lie parallel to the vertebrae. 



The outer border is smooth and even, except at its posterior third, 

 where a slight depression for the ureter exists ; the inner border 

 has usually two or three well-marked notches, the hindermost of 

 which is the deepest (Fig. 215). Each notch is continued outwards 

 as a groove, traversing the whole breadth of the ventral surface 

 and containing a branch of the renal portal vein. The ventral 

 surface is, as a whole, slightly concave, grooved, and lobulated ; 

 the dorsal surface is smooth and slightly convex. 



b. [Minute structure. The kidney is enclosed in a thin capsule 

 of fibrous tissue (Fig. 220 Jig), which sends in fine trabeculae to 

 support the glandular structures and the blood-vessels.] 



( i ) The blood-vessels of the kidney are the renal veins, the renal 

 arteries, and the renal portal vein. 



a. The renal portal vein (p. 247) courses along the outer border 

 of the posterior part of the kidney, and then along the outer margin 

 of the dorsal surface ; in this course it gives off large branches, 

 which course inwards and forwards and supply numerous lateral 

 twigs. These anastomose to form a network of vessels on the 

 dorsal surface of the organ, from which very numerous large 

 branches course downwards and somewhat inwards to join corre- 

 sponding branches of the renal veins (Fig. 216 I). 



