DISSECTION OP THE BACK AND THORAX. 



125 



and the clots of blood having been cleared out, the cavity will be 

 ready for examination. 



The Cavity of the Right Auricle. The interior of this and the 

 other cavities of the heart is smooth and glistening in virtue of an 

 endothelial membrane termed the endocardium, which is here continuous 

 with the endothelial lining of the great veins. It will be observed that 

 the muscular wall of the avu-icle is thrown into parallel ridges, which 

 from their resemblance to the 

 teeth of a comb are termed 

 musculi ])ectinati. The venous 

 orifices by which the blood is 

 poured into the cavity are all 

 found in the sinus venosus, 

 and are as follows : — 1. The 

 anterior vena cava empties 

 itself into the anterior part of 

 the roof of the sinus. 2. The 

 posterior vena cava discharges 

 itself at the lower and back 

 part of the outer wall of the 

 sinus. 3. The coronaiy ven- 

 ous sinus conveys the blood 

 from the wall of the heart it- 

 self, and its mouth will be 

 found under that of the pos- 

 terior vena cava. 4. The vena 

 azygos sometimes has an in- 

 dependent opening into the 

 auricle, and it then discharges 

 itself by the roof of the sinus, 

 behind the mouth of the 

 anterior cava. At other times 



Fig. 9. 



Diagram of the two Cavities of the right side 

 OF THE Heart (Ellis). 



a. Anterior cava ; b. Posterior cava ; c. Right auriculo- 

 ventrioular opening ; d. Fossa ovalis ; e. Opening of 

 the coronary sinus ; /'. Foramina Thebesii, the openings 

 . , , , , . of veins ; rt. Aperture of the pulmonary artery ; h. 



it opens into the anterior Auricular- appendix. 



cava. 5. The vence co7'dis 



minivice are small veins of the wall of the right auricle, which, instead 



of discharging themselves by the coronary sinus, open directly on 



the wall by minute mouths named the foramina Thebesii. Of all 



these orifices, that of the coronary sinus is the only one provided with 



a valve. It is a thin fold of the lining membrane, termed the valve of 



Thebesius. 



The inner wall of the sinus venosus is formed by the auricular sep- 

 tum, which is the partition between the two auricles. On this the 

 following objects are to be noticed : — 1. Between the orifices of the 

 anterior and posterior cavse is a muscular prominence — the tubercle of 



