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PHYSIOLOGY 



or by direct excitation of the internal surface of the uterus, in consequence 

 of movements of the foetus. In many cases no antecedent stimulus can be 



FIG. 565. Diagrammatic outline of the organs of circulation in the 



foetus of six months. (After ALLEN THOMSON. 1 



RA, right auricle of the heart ; nv, 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 ; vet, 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 ori- 

 fices ; da, opposite to the one passing through the pulmonary artery marks the place 

 of the ductus arteriosus ; a similar arrow-line is shown passing f roni the inferior vena 

 cava 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 ; uc, umbilical cord cut short ; ii', iliac 



discovered, and the automatic contraction of the uterus seems to be analo- 

 gous to that which occurs in the distended bladder. These contractions 



