EIGHT AURICLE. 389 



dog, being called the auricles, the inferior the ventricles. These 

 divisions are marked externally by deep grooves, in which the 

 cardiac blood-vessels run, and which are generally filled with fat. 

 Two of these grooves extend from the base of the ventricles to 

 the apex of the heart, and correspond to the internal septum ; 

 they are called the anterior and posterior longitudinal furrows. 

 Around the base of the ventricles is a deep transverse auriculo- 

 ventricular furrow, which marks the division of the heart into 

 an upper or auricular, and a lower or ventricular portion. 



The right side of the heart is sometimes called the venous, the 

 left the arterial side, named from the kind of blood which passes 

 through them. We will describe first the cavities of the right 

 side, and then those of the left. 



RIGHT AURICLE. 



The right auricle is the larger, and forms the right and 

 anterior portion of the base. It consists of two portions ; the 

 sinus venosus, or principal cavity, is somewhat quadrangular ; its 

 walls are thin, and connected inferiorly with the right ventricle ; 

 internally, with the left auricle ; anteriorly, they are prolonged 

 to form the appendix. The appendix auriculce, or proper 

 auricle, is a small conical pouch, which projects forwards from 

 the sinus ; its walls are thick, and its edges, more particularly 

 the outer one, serrated. On laying open the interior of the 

 auricle (which is best done by an incision from the appendix to 

 the mouth of the posterior vena cava, then opening the anterior 

 cava, and connecting the incisions), the smooth transparent 

 Endocardium or lining membrane, anterior and posterior Venae 

 cavae. Coronary sinus. Foramina Thebesii, and right Auriculo- 

 ventricular opening are displayed. 



The anterior vena cava returns the blood from the. anterior 

 part of the body, and opens into the supero-posterior part of the 

 sinus venosus. The posterior cava, which returns the blood 

 from the posterior region of the body, opens into the infero- 

 posterior part of the external wall of the sinus, near the inter- 

 auricular, or superior part of the longitudinal septum. The 

 coronary sinus, the dilated termination of the larger coronary or 

 cardiac veins, is situated below the opening of the posterior cava, 

 between it and auriculo- ventricular opening ; and through it the 

 blood is returned from the substance of the heart. The coronxjbry 



