800 THE F(ETAL CIRCULATION. 



border of the fossa, converts the aperture into an oblique passage or 

 slit over the valvular margin of the fold, so that in the last three and a 

 half months the arrangement is completed, by which blood may readily 

 pass from the right into the left auricle, but not in a contrary direction. 



The Eustachian Valve constitutes a crescentic fold of the lining 

 structure of tlie heart, which is situated to the right of the opening of 

 the inferior vena cava and fossa ovalis, deepens that fossa, and directs 

 the blood entering it from the inferior cava towards the opening of the 

 foramen ovale ; while it throws the opening of the great coronary vein 

 into connection with the right auricle, into which the superior vena 

 cava also opens. 



The formation at an early period of foetal life of the transverse vein 

 of the neck uniting the left with the right brachio-cephalic veins, 

 carries the whole of the blood returning from the head and neck, toge- 

 ther with that from the main azygos, into the stream entermg the heart 

 by the superior cava. 



The ductus arteriosus passes from the main pulmonary artery into 

 the aorta, at the hollow part of the arch, a short distance beyond the 

 place of origin of the left subclavian artery. It is nearly of the same 

 width with the pulmonary stem, while the right and left pulmonary 

 arteries are of comparatively small size, so long as the lungs have 

 not been expanded by air in rfespiration. 



TTmbilical Vessels. — Besides tlie usual branches of the descending aorta 

 intended to supply the abdominal viscera and the lower limbs, two large vessels, 

 named hypogastric or iimhilical arteries, are prolonged from the common iliacs, 

 and passing out of the abdomen, proceed along the umbilical cord, coiling round 



Fig. 597. — Semi-diageammatic view of the Organs of Circulation in the Fcetus 

 FROM BEFORE (from Luschka, modified, and from Nature). | 



a, front of the thyroid cartilage ; 6, right side of the thyroid body ; c, trachea ; d, 

 surface of the right lung turned outwards from the heart ; e, diai^hragm below the apex 

 of the heart ; /, right lobe of the liver, dissected to show ramifications of the portal and 

 hepatic veins ; /', the middle part and left lobe of the liver in the same manner, .showing 

 branches of the umbilical veins and ductus venosus ; g, right, fj', left kidney ; ij" , suin-a- 

 renal bodies ; h, right, li, left ureter ; i, portion of the small intestine tunied towards 

 the side, to show the veins from it going to the portal vein ; Ic, urinary bladder ; I, is 

 placed below the umbilicus, which is turned towards the left of the fcetus, and points by 

 a line to the urachus ; m, rectum, divided and tied at its upjier part. 



A, A. right auricle of the heart opened to show the foramen ovale : a probe, intro- 

 duced through the large divided right hepatic vein and vena cava inferior, is seen passing 

 through the fossa ovalis into the left auricle : at the lower part of the fossa ovalis is seen 

 the Eustachian valve, to the right and inferioi'ly the auriculo-ventricular orifice ; B, the 

 left auricular appendix ; C, the surface of the right ventricle ; D, placed on the inner 

 surface of the left lung, i)oints to the left ventricle. 



1, ascending part of the arch of the aorta ; 1', back part beyond the ductus arteriosus ; 

 1", abdominal aorta; 2, stem of the pulmonary artery ; 2', the place of division into right 

 and left pulmonary arteries and root of the ductus arteriosus : the left pueumo-gastric 

 nerve is seen descending over the arch of the aorta ; 3, superior vena cava ; 3', right, 3", 

 left innominate vein ; 4, stem of the inferior vena cava, between the junction of the 

 hepatic vein and the right auricle ; 4', continuation of the vena cava inferior below ; 5, 

 umbilical vein within the body of the fojtus ; 5 x , without the bo'ly, in the umbilical 

 cord ; 5', 5', ductus venosus ; between 5 and 5', the direct branches of the umbilical vein 

 to the liver ; 5", 5", hepatic veins, tlu-ough one of which a probe is passed into the fossa 

 ovalis and through the foramen ovale ; 6, vena portD3 ; 6', its left branch joining the 

 umbilical vein; (i", its right branch; 7, placed on the right iliac vein, points to the right 

 common iliac ai-tery; 7', left common iliac artery; 8, right, 8', left umbilical arteries 

 coming from the internal iliac arteries ; 8 x , umbilical arteries without the body, in the 

 umbilical cord ; 9, 9', external iliac arteries ; 10, placed below the right renal vessels ; 

 11, inferior mesenteric artery, above the root of which .ore seen the two spermatic arteries. 



