68 



THORAX 



Orifice of superior 

 vena cava 



Crista terminalis 



Intervenous 

 tubercle 



Fossa ovalis 



Left atrio- 

 ventricular orifice 



(O.T. annulus ovalis), which lies on the inter-atrial septum 

 and forms the anterior and upper boundary of a shallow 

 fossa, the fossa ovalis. At the upper end of this fossa there 

 was, during foetal life, a foramen, the foramen ovale, through 



which the two atria 



Superior vena cava Communicated With 



each other. The 



Right auricle (O.T. appendix) object of the Valve 



of the vena cava, 

 which in foetal life 

 was much more 

 perfect, was to di- 

 rect the oxygenated 

 inferior caval blood 



Limbus ovalis through the fora- 

 men ovale into the 

 left atrium, whence 

 it was passed into 

 the left ventricle, 

 and was then dis- 



c? r g y sinus tributed, by the 



Coronary valve aorta, throughout 



inferior the whole system. 



caval valve 



(Eustachian) During foetal life it 



would have been use- 

 less to pass the blood 

 through the lungs, 

 which were inactive and 

 devoid of air. At the 



FIG. 34. Interior of Right Atrium as seen by the same time, had the 

 removal of the anterior wall, or that wall op- oxygenated blood been 

 posed to the base of the Ventricles. This is passed through the 

 a part of the same specimen that is depicted right atrium into the 

 in Fig. 31. 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 

 the upper curved end of the limbus ovalis. 



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. On its right margin lies a valvular fold, the valve of 



Cut edge of 

 atrial wall 

 Inferior vena cava 



