THE PIGEON 



413 



which there are altogether nine, named, from behind 

 forwards, the abdominals, posterior thoracics, anterior 

 thoracics, cervicals, and interclavicular. Certain of the 

 air sacs are connected with air spaces in the bones. 

 This arrangement adds somewhat to the lightness of the 



Fig. 303. — The urogenital organs 

 of a female pigeon. — From 

 Thomson. . 



AT., Kidney (metanephros) with three 

 lobes; «., ureter; cl., cloaca; ov., 

 ovary; od. t oviduct ; ft., funnel at 

 end of oviduct ; r.r.od., rudimentary 

 right oviduct. 



Fig. 304. — The urogenital 

 organs of a male pigeon. 

 — From Thomson. 



T., Testes ; V., base of inferior 

 vena cava; S.R., suprarenal 

 glands; JC, kidneys . with 

 three lobes (1, 2, 3) ; u., 

 ureter ; v.d., vas deferens ; 

 v.s. t seminal vesicle ; cl. r 

 cloaca. 



bird, but is probably of greater importance in raising the 

 efficiency of its respiration by increasing the flow of the air 

 through the bronchi. Respiration is brought about mainly 

 by expiration, not by pumping in air, as in the frog, or 

 active inspiration, as in the rabbit. The movements of 

 breathing consist in the rise and fall of the sternum, which 

 compresses the air sacs and lungs. 



