742 THE VASCULAR SYSTEM. 
On the left the auricle is limited by the oblique septum which separates it from 
the left auricle. The sulcus terminalis is a shallow groove on the surface of the 
right auricle, which passes from the front of the superior vena cava to the left of the 
inferior vena cava, and indicates the junction of the primitive sinus venosus with 
the auricle proper. 
The interior of the auricle is lined with a glistening membrane, the endocardium ; 
its walls are smooth, except anteriorly and in the auricular appendix where 
muscular bundles form a series of small vertical columns, the musculi pectinati. These 
terminate above in a crest, the crista terminalis, which corresponds in position with 
the sulcus terminalis externally. 
At the upper and back part of the cavity is the opening of the superior vena 
cava, devoid of a valve. At the lower and back part is the orifice of the inferior 
vena cava, bounded in front by the rudimentary Eustachian valve; and immedi- 
ately below the Eustachian valve, between it and the auriculo-ventricular orifice, 
Aorta 
Vena cava superior 
Pulmonary artery 
Upper right 
pulmonary vein Right auricular appendix 
Conus arteriosus 
Lower right 
pulmonary vein Anterior cusp of 
Musculi pectinati tricuspid valve 
Annulus ovalis 
Chord tendinewz 
Fossa ovalis - 
Eustachian valve 
Moderator band 
Vena cava inferior 
Coronary (Thebesian) valve 
Musculi papillares 
Fic, 548,—THe CAVITIES OF THE RIGHT AURICLE AND RIGHT VENTRICLE OF THE HEART. 
is the opening of the coronary sinus, guarded by the Thebesian valve. The 
auriculo-ventricular aperture, guarded by a tricuspid valve, is known as the 
tricuspid orifice. It is situated in the antero-inferior boundary, and admits three 
fingers. A number of small fossee, foramina Thebesii (foramina venarum minimarun), 
are scattered over the walls, and some of these present at their apices the apertures 
of small veins, the vene minimi cordis. In the septal wall is an oval depression, 
the fossa ovalis, bounded above and in front by a raised margin, the annulus 
ovalis (limbus fosse ovalis), which is continuous inferiorly with the Eustachian 
valve; this fossa is the remains of an aperture, the foramen ovale, through which 
the two auricles communicated with each other before birth, and even in the 
adult a portion of the aperture persists at the upper part of the fossa in about one 
in five cases. Between the apertures of the superior and inferior ven cave, and 
behind the upper part of the fossa ovalis, a small eminence may be distinguished, 
which is called the tubercle of Lower (tuberculum intervenosum) ; in the foetus 
it probably directs the blood from the superior vena cava to the tricuspid orifice. 
