THE PIGEON 



415 



Pc.v 



with the active life of the bird and the rapid metabolism 

 Blood v s 1 w hi c h it necessitates. We have already seen 

 how the respiratory organs provide the ample 

 supply of oxygen which such 

 metabolism demands. The red 

 corpuscles are oval and nucleated. 

 The heart has four chambers, two 

 auricles and two ventricles, there 

 being no sinus venosus or conus 

 arteriosus. The impure blood 

 returned by the venae cavse to the 

 right auricle passes into the right 

 ventricle through an opening 

 guarded by a muscular valve 

 without chordae tendinese. It is 

 then driven by the pulmonary 

 artery to the lungs, whence it 

 returns by the pulmonary veins 

 to the left auricle, passing thence 

 through two membranous valves 

 with chordae tendinese to the left 

 ventricle, by which it is driven 

 into the single aortic arch. The 

 openings of the aorta and pul- 

 monary artery are guarded each 

 by three semilunar valves. The 

 aortic arch bends over to the 

 right side, giving off at its apex 

 right and left innominate arteries, 

 from each of which arise a carotid 

 and a subclavian. The latter is 

 exceedingly short, breaking up 

 immediately into brachial and 

 pectoral branches. The further 

 course of the arteries is shown 

 in the diagram (Fig. 305). The 

 venous system is shown in the 

 same figure. There are three 

 venae cavae, as in the frog. Each 

 superior vena cava is formed by 

 the union of a jugular, a brachial, 



Fig. 305. — A diagram of the 

 principal arteries and 

 veins of a pigeon. — From 

 Thomson, after Parker. 



ao., Aortic arch ; Br.a., brachial 

 artery ; Br.v. t brachial vein ; 

 C, carotid artery ; cm., 

 coccygeo-mesenterjc vein ; 

 d.a. , dorsal aorta ; F. , femoral 

 vein adjoining femoral artery ; 

 k.v. t hepatic veins ; il., in- 

 ternal iliac artery and vein ; 

 i.v.c, inferior vena cava,;y., 

 jugular vein ; La., left auricle; 

 P., right pulmonary artery J 

 Pea., pectorabartery ; 'Pc.v., 

 pectoral vein'; r.a., right 

 auricle; r.p. , hypogastric vein ; 

 tv. r renal vein'; sc, sciatic 

 artery and vein. Near the 

 apex of' the ventricle the 

 cceliac and anterioj mesenteric 

 arteries and the epigastric 

 vein are shown, but*- hot 

 lettered. At the hinder end 

 of the figure the caudal and 

 posterior mesenteric vessels 

 are shown, but not lettered. 



