234 



VASCULAK SYSTEM 



s 



the vena portse, and the umbilical vein ; and, as already noticed, reaches the right 



auricle through the trunk of the inferior cava. 



Of the blood entering 

 the heart by the inferior 

 vena cava, it is supposed 

 that only a small part is 

 mingled with that of the 

 superior cava, so as to pass 

 into the right ventricle ; by 

 far the larger portion is 

 thought to be directed 

 by the Eustachian valve 

 through the foramen ovale 

 into the left auricle, and 

 thence, together with the 

 small quantity of blood 

 returned from the lungs by 

 the pulmonary veins, to 

 pass into the left ventricle, 

 whence it is sent into the 

 arch of the aorta, to be 

 distributed almost entirely 

 to the head and upper 

 limbs. 



In earlier stages of 

 development than those 

 above described, it is cer- 

 tain that there is little or 

 no separation of the two 

 lands of blood, for both the 

 umbilical veins from the 

 placenta and the veins from 

 the yolk-sac and body gene- 

 rally, pour their blood 

 together into the sinus 

 venosus, and the mixed 

 blood is then forced through 

 a single somewhat narrowed 

 orifice (porta vestibuli of 

 His) into the auricle. 



FIG. 291. DIAGRAMMATIC OUTLINE OF THE ORGANS OF CIRCULA- 

 TION IN THE FCETUS OF six MONTHS. (Allen Thomson.) - 



EA, right auricle of the heart ; E V, right ventricle ; LA, left 

 auricle; Ev, Eustachian valve; LV, left ventricle; ;L, liver; 

 K, left kidney ; I, portion of small intestine ; a, arch of the aorta ; 

 a', its dorsal part ; a", lower end ; vcs, superior vena cava ; 

 <vci, inferior vena where it joins the right auricle ; vci', its 

 lower end; s, subclavian vessels ;j, right jugular vein ; c, common 

 carotid arteries ; four curved dotted arrow lines are carried through 

 the aortic and pulmonary opening and the auriculo-ventricular 

 orifices ; da, opposite to the one passing through the pulmonary 

 artery, marks the place of the ductus arteriosus ; a similar arrow 

 line is shown passing from the vena cava inferior through the 

 fossa ovalis of the right auricle, and the foramen ovale into the 

 left auricle ; hv, the hepatic veins ; 'vp, vena portse ; x to 

 vci, the ductus venosus ; uv, the umbilical vein ; ua, umbilical 

 arteries ; nc, umbilical cord cut short ; i, i', iliac v< 



CHANGES IN THE CIR- 

 CULATION AT BIRTH. 



The changes which occur 

 in the organs of circulation 

 and respiration at birth, 

 and which ] ead to the estab- 

 lishment of their perma- 

 nent condition, are more 

 immediately determined by 

 the inflation of the lungs 



1 In this diagram the arteries are conventionally coloured red and the veins blue, but these colours 

 are not intended to indicate the nature of the blood conveyed by the respective vessels. 



