PECULIARITIES OF THE FCETAL ORGANS OF CIRCULATION. 155 



right auricle, an arrangement which is also met with in birds and in certain 

 mammals, and which results from the vessels of the left side being developed 

 similarly to those of the right, while the cross branch remains small or absent. 



A case is recorded by Gruber in which the left vena azygos opened into the 

 coronary sinus, and was met by a small vein descending from the union of the 

 subclavian and jugular. Here, then, the jugular veins had been developed in the 

 usual manner, while the left vena azygos continued to pour its blood into the duct 

 of Cuvier. 



PECULIARITIES OF THE FCETAL ORGANS OF CIRCULATION. 



It may be useful here to recapitulate shortly the peculiarities of structure 

 existing in the advanced stage of the formation of the foetal organs of circulation, 



Fig. 188. DIAGRAMMATIC OUTLINE OP THE 



ORGANS OP CIRCULATION IN THE F(ETUS 



OP six MONTHS. (Allen Thomson.) 



RA, right auricle of the heart ; EV, 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, in- 

 ferior 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 th'e 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 t vena portse ; x to 

 vci, the ductus venosus ; uv, the umbilical 

 vein ; ua, umbilical arteries ; uc, umbilical 

 cord cut short ; i i', iliac vessels. 



with reference to their influence in 

 determining the course of the blood 

 during intra-uterine life, and the 

 changes which occur in them upon 

 the establishment of pulmonary re- 

 spiration at birth. 



The foramen ovale retains the 

 form of a free oval opening in the 

 septum atriorum up to the fourth 

 month, but in the course of that 

 month and the next the growth of 

 the valvular plate which fills up the 

 floor of the fossa ovalis, becomes 

 complete, so that in the last three 

 and a half months the blood can 

 only pass from the right into the left 

 auricle, not in a contrary direction. 



The Eustachian valve constitutes a crescentic fold of the lining structure of 

 the heart, which is so situated as to direct the blood entering the auricle by the 

 inferior cava towards the opening of the foramen ovale. 



