THE CIRCULATION 153 



18. The Heart. The heart is the central engine of the cir- 

 culation. In this wonderful little organ, hardly larger than 

 a man's fist, resides that sleepless force by which, during the 

 whole of life, the current of the blood is kept in motion. It 

 is placed in the middle and front part of the chest, inclining 

 1 o the left side. The heart-beat may be felt and heard between 

 the fifth and sixth ribs, near the breast-bone. The shape of 

 the heart is conical, with the apex or point downward and in 



the liver, pancreas, arid other organs perform their functions with more 

 vigor." Lankester's Manual of Health. 



6. Experiment. The Heart. To demonstrate the physiological 

 anatomy of the heart will require some dissecting, and a little more care 

 and work than the other experiments, but the teacher will be fully 

 rewarded by the close attention and great interest shown by the pupils. 



Obtain from your butcher a bullock's heart inclosed in the pericardium 

 or "bag." Instruct him to cut it out carefully and as high up as he can, 

 so as not to injure it, and so as to leave of the large blood-vessels as much 

 attached as is possible. 



Cut away all the fat surrounding the heart and great blood-vessels ; 

 cut open the pericardium from apex to base, and partly away from the 

 latter, so as to give room for exposing the cavities of the heart. The 

 latter should be opened by two incisions along the septum separating the 

 right from the left heart. The incision should run from apex to base, 

 laying open both ventricle and auricle. Cut open all the large vessels 

 found at the base, into the cavities to which they lead. 



Going from without inward observe and explain the different parts as 

 follows : 



1. THE PERICARDIUM. Note its structure and smooth, shining inner 

 surface. Show how it surrounds the heart, and how it is attached along 

 the base and great blood-vessels. 



2. GENERAL STRUCTURE OF THE HEART. Show the thin-walled auri- 

 cles ; the difference between the thickness of the walls of the ventricles ; 

 the difference in structure between the arteries and veins; demonstrate 

 the two coronary arteries and their accompanying veins. 



3. RIGHT AURICLE AND VENTRICLE. Demonstrate the venae cavae and 

 their entrance into the auricle ; the auriculo-ventricular valves between 

 the two cavities ; the structure, attachment, and action of the valves ; the 

 pulmonary artery. 



4. LEFT AURICLE AND VENTRICLE. Demonstrate the pulmonary veins 

 and their entrance into the auricle ; the mitral valve between auricle and 

 ventricle ; the aortic valve, its structure, action, and attachment ; the 

 structure and great strength of the aorta. 



18. Office of the heart ? Location of the heart ? Its beat ? Its shape ? Protection to 

 the heart ? What else is said in relation to the heart ? 



