THE FROG. 83 



with the anterior abdominal vein by a large vessel 

 (systeviico-portal anastomosis). 



Note that it is formed by the union of those vessels 

 bringing back the blood from the alimentary canal 

 and its appended glands (its factors may be better 

 studied in detail later on). 



Frequently, but not invariably, some of the veins 

 {^gastric vems) which carry back the blood from the 

 stomach, enter the liver independently of the rest. 



The renal portal veins. 



Remove sufficient of the alimentary canal to fully 

 expose the kidneys. The above-named veins will 

 be seen skirting the outer borders of the same ; that 

 of one side may be examined in detail. 



a. Its origin; when traced back it is seen to arise, 

 side by side with the pelvic vein (i. a.) from the 

 bifurcation of a vessel which skirts the outer 

 border of the thigh {femoral vein). 



b. Its distribuiion ; on reaching the kidney it is seen 

 to break up into a number of afferent renal veins^ 

 for distribution to that organ. 



c. Its re7naining factors. 



a. The sciatic vein; a large vessel seen, on 

 carefully dissecting away the hip-girdle, to bring 

 in the blood from the deeper parts of the hind- 

 limb. 



^. The dorso-lunibar vein; a well-defined vessel 

 joining it anteriorly on a level with the kidney ; 

 it brings back the blood from the body-wall 

 adjacent. 



y. The oviducal veins ; two or three vessels entering 

 it (in the female) immediately behind /?. 



6—2 



