682 DEVELOPMENT OF THE CIRCULATORY APPARATUS. 



Fig 272. 



passes through the right auricle downward into the right ventricle, 

 thence through the pulmonary artery and ductus arteriosus, into 

 the thoracic aorta, while the blood of the inferior vena cava, enter- 

 ing the left auricle, passes into the left ventricle, thence into the arch 

 of the aorta, and is distributed to the head and upper extremities, 

 before reaching the situation of the arterial duct. The two streams, 

 therefore, in passing through the heart, cross each other both behind 

 and in front. The venous blood, returning from the head and 



upper extremities by the superior 

 vena cava, passes through the abdo- 

 minal aorta and the umbilical arte- 

 ries, to the lower part of the body, 

 and to the placenta ; while that re- 

 turning from the placenta, by the 

 inferior vena cava, is distributed to 

 the head and upper extremities, 

 through the vessels given off from 

 the arch of the aorta. 



This division of the streams of 

 blood, during a certain period of 

 foetal life, is so complete that Dr. 

 John Eeid, 1 on injecting the infe- 

 rior vena cava with red, and the 

 superior with yellow, in a seven 

 months' human foetus, found that 



the red had passed through the foramen ovale into the left auricle 

 and ventricle and arch of the aorta, and had filled the vessels of 

 the head and upper extremities; while the yellow had passed into 

 the right ventricle, pulmonary artery, ductus arteriosus, and tho- 

 racic aorta, with only a slight admixture of red at the posterior 

 part of the right auricle. All the branches of the thoracic and 

 abdominal aorta were filled with yellow, while the whole of the red 

 had passed to the upper part of the body. 



We have repeated the above experiment several times on the 

 foetal pig, when about one-half and three-quarters grown, first taking 

 the precaution to wash out the heart and large vessels with a wa- 

 tery injection, immediately after the removal of the foetus from the 

 body of the parent, and before the blood had been allowed to coagu- 

 late. The injections used were blue for the superior vena cava, 



Diagram of CIRCULATION THROUGH 

 THE F<ETAL HKART. a. Superior vena 

 cava. b. Inferior vena cava. c, c, n, c. Arch 

 of aorta aud its branches, d. Pulmonary 

 artery. 



Edinburgh Medical and Surgical Journal, vol. xliii. 1835. 



