LECT. XVII. 



THE CIRCULATION. 



313 



a correct notion of the way in which this function is per- 

 formed, it is sufficient to expose the heart of a rabbit or 



Fig. 23. 



The Anatomy of the Heart; 1, the right auricle; 2, the entrance of the superior 

 venacava; 3, the entrance of the inferior cava ; 4, the opening of the coronary vein, 

 half closed by the coronary valve; 5, the Enstachian valve ; 6, the fossa ovalis, sur- 

 rounded by the annulis ovalis; 7, the tuberculum Loweri ; 8, the musculi per.tinati 

 in the appendix auricula;; 9, the auriculo-ventricular opening; 10, the cavity of the 

 right ventricle; 11, the tricuspid valve, attached by the chordae tendineae to the car- 

 neae column; (12) 13, the pulmonary artery guarded at its commencement by three 

 semilunar valves; 14, the right pulmonary artery, passing beneath the arch and be- 

 hind the ascending aorta ; 15, the left pulmonary artery, crossing in front of the 

 descending aorta ; *, the remains of the ductus arteriosus, acting as a ligament 

 between the pulmonary artery and arch of the aorta ; the arrows mark the course 

 of the venous blood through the right side of the heart; entering the auricle by 

 the superior and inferior cava, it passes through the auriculo-ventricular opening 

 into the ventricle, and thence through the pulmonary artery to the lungs; 16, the 

 left auricle ; 17, the openings of the four pulmonary veins ; 18, the auriculo-ventricu- 

 lar opening; 19, the left ventricle; 20, the mitral valve, attached by its chordas ten- 

 dinere to two large columns carnese, which project from the walls of the ventricle; 

 21, the commencement and course of the ascending aorta behind the pulmonary ar- 

 tery, marked by an arrow; the entrance of the vessel is guarded by three semilu- 

 nar valves ; 22, the arch of the aorta. The comparative thickness of the two ven" 

 tricles is shown in the diagram. The course of the arterial blood through the left 

 side of the heart is marked by arrows. The blood is brought from the lungs by the 

 four pulmonary veins into the left auricle, and passes through the auriculo-ventri- 

 cular opening into the left ventricle, whence it is conveyed by the aorta to every 

 part of the body. 



