DISSECTION OF THE BACK AND THORAX. 



127 



mus conveys the blood from the wall of the heart itself, and its mouth 

 vill be found under that of the posterior vena cava. 4. The vena 

 izygos sometimes has an independent opening into the auricle, and it 

 hen discharges itself by the roof of the sinus, behind the mouth of the 

 interior cava. At other times it opens into the anterior cava. 5. The 

 mnai cordis minimce are small veins of the wall of the right auricle, 

 vhich, instead of discharging themselves by the coronary sinus, open 

 lirectly on the wall by minute 

 nouths named the foramina 

 Vhehesii. Of all these oriiices, 

 hat of the coronary sinus is 

 he only one provided with a 

 'alve. It is a thin fold of the 

 ining membrane, termed the 

 Ktlve of Thehesius. 



The inner wall of the sinus 

 'enosus is formed by the 

 .urioular septum, which is the 

 •artition between the two 

 .uricles. On this the follow- 

 ng objects are to be noticed : — 

 . Between the orifices of the 

 .nterior and posterior cavse is 

 . muscular prominence — the 

 ubercle of Lower. 2. Above 

 nd in front of the opening of 

 he posterior cava is a depres- 

 ion of the septum that looks 

 ke another venous orifice, 

 'his is the fossa ovalis, and it 

 larks the former position of 

 he foramen ovale — an aperture 

 'hich, in the foetus, estab- 

 shed a communication be- 



ween the right and left auricles. The raised border which surrounds 

 le fossa is termed the annulns ovalis. In the foetus of many animals, 

 at not of the horse, a valve, termed the Eustachian valve, directs the 

 lood from the posterior cava through the foramen ovale. After birth 

 le foramen ovale in nearly every case becomes completely closed, but 

 )metimes an oblique slit remains, which, however, does not necessarily 

 ermit any blood to pass through the septum. 



The blood which passes through the right auricle is venous in char- 

 ;ter. It has been circulating among the tissues, and it is poured into 

 le cavity at the venous orifices already enumerated. When the auricle 



Fig 9. 



DiAGRAil OF THE TWO CavITIE.S OF THE RIGHT 

 SIDE OF THE HeART (£Uis). 



a. Anterior cava ; b. Fosterior cava ; c Right 

 auriculo - ventricular opening ; d. Fossa ovalis ; 

 e. Opening of tlie coronary sinus ; /. Foramina 

 Tliebesii, the opening of veins; g. Aperture of the 

 pulmonary artery ; h. Auricular appendix. 



