THORACIC CAVITY 93 



it was passed into the left ventricle, and was then distributed, 

 by the aorta, throughout the whole body. 



During foetal life it would have been useless for the blood to pass through 

 the lungs, which were inactive and devoid of air. At the same time, had 

 the oxygenated blood, which is poured into the upper part of the inferior 

 vena cava by the vein from the placenta, passed through the right atrium 

 into the right ventricle, it would have failed to reach the head and 

 the upper extremities, for, leaving the right ventricle by the pulmonary 

 artery, it would have entered the aorta through the ductus arteriosus 

 beyond the origin of the left subclavian artery and, therefore, beyond the 

 innominate and left common carotid arteries. 



In many cases a small part of the foramen ovale persists 

 in the adult. If it is present it will be found on the left of 



Pulmonary artery Aorta 



Right end of transverse sinus 

 rtery 



Left end of 

 transverse sinus 

 Left auricle 



Left atrium ^ Right atrium 



^^^ Transverse sinus 

 Interatnal septum 



FIG. 45. Transverse section through the Upper Part of the Heart. 



the upper curved end of the limbus ovalis, and a probe should 

 be passed through it into the left atrium. 



The opening of the coronary sinus lies to the left of the lower 

 end of the limbus ovalis and directly posterior to the tricuspid 

 orifice, through which the right atrium communicates with 

 the right ventricle (Figs. 42, 44). On its right margin lies a 

 valvular fold, the valve of the coronary sinus (Thebesii), 

 which turns the blood, flowing from left to right in the 

 sinus, forwards into the atrio-ventricular orifice. The venae 

 cordis minimae and the anterior cardiac veins open directly 

 into the atrium by small orifices scattered irregularly over 

 the walls. 



The tricuspid orifice is in the lower and anterior part of the 

 atrium. It opens forwards into the lower and posterior part of 

 the cavity of the right ventricle, and is sufficiently large to 

 admit the tips of three fingers. It is bounded by a fibrous 



