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HANDBOOK OF PHYSIOLOGY. 



from its base, but, excepting the base, the organ itself lies free in the 

 sac of the pericardium. The part which rests upon the diaphragm is 

 flattened, and is known as the posterior surface, whilst the free upper 

 part is called the anterior surface. The margin towards the left is 

 thick and obtuse, whilst the lower margin towards the right is thin and 

 acute. 



On examination of the external surface the division of the heart into 

 parts which correspond to the chambers inside of it may be traced, for 

 a deep transverse groove called the auriculo-ventricular groove divides 



FIG. 89. The right auricle and ventricle opened, and a part of their right and anterior walls 

 removed, so as to show their interior. %.-!, superior vena cava; 2, inferior vena cava; 2', he- 

 patic veins cut short; 3, right auricle ; 3', placed in the fossa ovalis, below which is the Eustachian 

 valve; 3", is placed close to the Aperture of the coronary vein ; +, +, placed in the auriculo ven- 

 tricular groove, where a narrow portion of the adjacent walls of the auricle and ventricle has been 

 preserved; 4, 4, cavity of the right ventricle, the upper figure is immediately below the semilunar 

 valves; 4', large columna carnea or musculus papillaris; 5, 5', 5", tricuspid valve; 6, placed in the 

 interior of the pulmonary artery, a part of the anterior wall of that vessel having been removed, 

 and a narrow portion of it preserved at its commencement, where the semilunar valves are attached ; 

 7, concavity of the aortic arch close to the cord of the ductus arteriosus; 8, ascending part or sinus of 

 the arch covered at its commencement by the auricular appendix and pulmonary artery; 9, placed 

 between the innominate and left carotid arteries; 10, appendix of the left auricle; 11, 11, the outside 

 of the left ventricle, the lower figure near the apex. (Allen Thomson.) 



the auricles which form the base of the heart from the ventricles which 

 form the remainder, including the apex, the ventricular portion being by 

 far the greater; and, again, the inter-ventricular groove runs between 



