RIGHT AURICLE. 389 



the ears of a 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 

 more or less filled with fat. Two of these grooves extend from 

 the base of the ventrifcles to the apex of the heart, and correspond 

 to the internal septum ; they are called the anterior and pos- 

 terior longitudinal furrows. Around the base of the ventricles 

 is a deep transverse auriciilo-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 those of the right 

 ventricle ; internally, with those of the left auricle ; anteriorly, 

 they are prolonged to form the appendix. The appendix auric- 

 ula}, or pro23er 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 trans- 

 parent Endocardium or lining membrane, anterior and posterior 

 Vense cavse. Coronary sinus. Foramina Thebesii, and right Auri- 

 culo-veutricular 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 coronary 



