QUESTIONS AND ANSWERS 63 



Describe the right and left heart, noting the size of the different cavi- 

 ties, the thickness of the walls at different points, the nature, 

 position and dependencies of the four sets of valves and 

 the source and distribution of the vascular and nervous 

 supply. 



The heart is divided by a vertical septum into two parts, which 

 are further divided into four by a transverse septum. The cavities 

 above the transverse septum are called right and left auricles, those 

 below, the right and left ventricles, the two latter constituting the 

 largest portion of the heart. 



The right auricle : The walls are about one-fourth of an inch in 

 thickness. It receives the anterior vena cava, posterior vena cava, 

 vena azygos, and the large coronary veins. It opens, in its floor, into 

 the right ventricle through the auriculoventricular opening. 



The right ventricle : Its walls are on an average six-tenths of an 

 inch thick. It has two openings, the auriculoventricular, and the 

 pulmonary opening into the pulmonary artery. 



The left auricle : Similar to the right. The waUs are irregular 

 in thickness, varying from one-third of an inch in some places to a 

 very thin membranous wall in others. It receives the pulmonary 

 veins and empties through the auriculoventricular opening in its 

 floor into the left ventricle. 



The left ventricle : Its walls are on an average one and one-fifth 

 to one and five-eighths inches in thickness. Two openings, the 

 auriculoventricular and aortic. 



The valves of the heart are made of fibrous segments. The right 

 auriculoventricular is composed of three segments (tricuspid) 

 attached by their free edges to the ventricular wall by tendinous 

 cords, chordae tendinae. The left auriculoventricular is composed 

 of two segments (bicuspid) and is similarly attached. The pul- 

 monary and aortic openings of the ventricles are closed by the semi- 

 lunar valves made up of three segments which are also attached 

 by tendinous cords. 



The blood supply of the heart is by the two coronary arteries, 

 branches from the trunk of the aorta at the sigmoid valves. Each 

 divides into two principal branches, one passing along the horizontal, 

 the other in the vertical furrow of the heart. The venous blood is 

 returned to the right auricle by the coronary vein. 



The nerves of the heart, furnished by the cardiac plexus, come 

 from the pnetunogastric and sjonpathetic. 



Mention all the arteries given off from the posterior aorta. 



Intercostals, phrenic, lumbar, middle sacral, broncho-oesophageal, 

 cceliac axis, anterior mesenteric, posterior mesenteric, renal, sper- 



