460 



COMPARATIVE ANATOMY 



region : it has the latter position, for instance, in most Reptiles 

 (Figs. 345, 357, 358) and all Birds (Fig. 346). The posterior 

 end of the kidney, which is generally narrower than the rest, 

 may even extend under the root of the tail, as in Lacerta, in 

 which region the two organs are fused. 



Thus according to the position of the kidneys, the ureters 

 (metanephric ducts) either do not extend freely along the 



N 



FIG. 346. MALE URINOGENITAL APPARATUS OF HERON (Ardea cinerea). 



Ao, aorta; BF, bursa Fabricii, which opens into the cloaca at BF 1 ; Ep, epi- 

 didymis ; Ho, testis ; N, kidney ; Ur, ureter, opening into the cloaca (Cc) 

 at Sr ; V, V, furrows on the ventral surface of the kidney in which veins lie 

 embedded ; Vd, vas deferens, which opens at Vd l on a papilla in the cloaca. 



body-cavity, or they may have a longer or shorter free course. 

 The latter is the case, for instance, in Crocodiles, and more 

 especially in Birds (Fig. 346) : in the latter the kidneys 

 are closely embedded within the pelvis, and their ventral 

 flattened surface is usually divided into lobes and is often 



