In the dorsal view (Fig. 116) the position of the ventricular septum is not indicated. On the surface of the left ventricle a short distance from the ventricular septum and nearly parallel to it are seen branches of the coronary artery and the coronary vein passing toward the apex. Craniad of the left ventricle is seen the left auricle (_b_) with the pulmonary veins (_g_, _h_, _i_) opening into it. Craniad of the right ventricle (_a_) is the right auricle (_c_) with the venæ cavæ (_d_ and _e_) opening into it near the middle. Coming from beneath the auricles are seen the pulmonary artery (_j_) and the aorta (_f_). The =chambers of the heart=. 1. The =right auricle= (atrium dextrum) (Figs. 115 and 116, _c_). Externally the right end of the right auricle projects so as to form its =auricular appendage= (Fig. 115, _c_) which lies at the right of the base of the aorta (Fig. 115, _g_). The superior vena cava (Fig. 116, _e_) is seen entering near the cranial end of the auricular septum opposite the base of the aorta. The inferior vena cava (Fig. 116, _d_) enters the auricle near the coronary sinus and close to the auricular septum. The netted appearance which the wall, especially that of the appendage, presents externally is due to the muscular thickenings of the wall (=musculi pectinati=). [Illustration: FIG. 115.--HEART, VENTRAL VIEW. FIG. 116.--HEART, DORSAL VIEW. Fig. 115.--_a_, right ventricle; _b_, left ventricle; _c_, right auricular appendage; _d_, left auricular appendage; _e_, conus arteriosus; _f_, pulmonary artery; _g_, aortic arch; _h_, thoracic aorta; _i_, vena cava superior; _j_, innominate artery; _k_, left subclavian artery; _l_, left common carotid; _m_, right common carotid; _n_, right subclavian; _o_, azygos vein; _p_, the two innominate veins; _q_, coronary artery. Fig. 116.--_a_, right ventricle; _b_, left auricle; _c_, right auricle; _d_, vena cava inferior; _e_, vena cava superior; _f_, aorta; _g_, _h_, _i_, groups of pulmonary veins (_g_, dorsal group; _h_, sinistral group; _i_, dextral group); _j_, pulmonary artery (division into two); _k_, innominate artery; _l_, left subclavian; _m_, left common carotid; _n_, right common carotid; _o_, right subclavian; _p_, azygos vein.] The cavity (including that of the auricular appendage) is somewhat egg-shaped, with its long axis transverse. The musculi pectinati, which branch and unite into a network, are most abundant on its dorsal wall at the right. The axes of the two venæ cavæ if produced into the cavity of the auricle would meet one another at its centre and nearly at right angles. Caudad of the opening of the inferior vena cava is seen the slit-like opening of the =coronary sinus=, guarded craniad by the semilunar =valve of the coronary sinus= (or valve of Thebesius). The coronary sinus receives blood from =coronary veins=, which collect it from the walls of the heart.