694 



HUMAN ANATOMY. 



faces, however, passing into one another almost insensibly without forming distinct 

 angles. Viewed externally, the roof of the chamber is directed upward, backward, 

 and somewhat to the right, and near its junction with what may be termed the poste- 

 rior wall receives the superior vena cava. The posterior wall, also smooth and 

 rounded, receives, near its junction with the median wall, the inferior vena cava, and 

 below and to the left of this, in the posterior auriculo-ventricular groove, is the ter- 

 minal portion of a vein which winds around the heart from the left and is termed the 

 coronary sirms. The antero-lateral wall is prolonged into a somewhat triangular 

 diverticulum with crenulated edges, which winds anteriorly around the proximal por- 

 tion of the systemic aorta and is known as the right auricular appendix (auricula 

 dextra). The median wall is not visible on surface view, and is formed by a rather 

 thin muscular partition, the auricular septum (septum atriorum), which is common to 

 both auricles ; and the floor, also invisible from the exterior, corresponds to the base 

 of the right ventricle, and is perforated by an oval aperture, the right auriculo-ven- 

 tricular orifice, which places the cavity of the auricle in communication with that of 



the right ventricle. 



Fig. 657. 4 



Vena azygos 



Superior 

 vena cava 



Right pulmo- 

 nary artery 



Sup. pulm. vein <^"~ 



Inf. pulm. vein 



Fossa ovalis, 

 surrounded 

 by annulus 



Inferior 

 vena cava 



Systemic aorta 



Pulmonary aorta or artery 



Right auricular appendage 



Right ventricle, conus 

 arteriosus 



Right auriculo- 

 ventricular 

 valve 



Orifice of coronary sinus, guarded by Thebesian valve 

 Eustachian valve Depiession receiving Thebesian veins 



Interior of right auricle exposed after removal of part of heart wall. 



When the interior of the right auricle is examined (Figs. 657, 661), the 

 surface is found to be for the most part smooth, being lined throughout by a delicate 

 shining membrane covered by flattened cells and termed the endocardium. The 

 general smoothness of the surface is, however, interrupted here and there by mmute 

 depressions (foramina venarum minimarum) into some of which open the orifices of 

 Thebesian veiiis that traverse the walls of the heart. The cavity of the auricular 

 appendix is crossed by a net-work of anastomosing fibro-muscular trabeculae, the 

 rmisculi pectinati, which are everywhere lined upon their free surfaces by endocardium 

 and give to the appendix a somewhat spongy texture. In the roof of the auricle is 

 seen the circular orifice of the superior vena cava, unguarded by valves and ha\ing a 

 diameter of from 18-22 mm., and on the posterior wall is the somewhat oblique 

 opening of the inferior vena cava, somewhat larger than that of the superior one, 

 measuring from 27-36 mm. in diameter. The lower and lateral margins of this 

 orifice are guarded by a crescentic fold, the Eustachian valve (valvula venae cavae 

 mferioris), which tends to direct the blood entering by the vein upward and medially, 

 and is the remains of a structure of considerable importance during fcctal life (page 



