246 



HUMAN PHYSIOLOGY 



from the roots of the blood-vessels. In the pericardium 

 is a small quantity of fluid. What we call the right side 

 of the heart is thrown to the front by a spiral twist of the 

 organ so we see chiefly this ventricle when the heart is 

 exposed from in front. The left ventricle is thrown 

 behind but the apex belongs to it; it may be said to be 



longer than the right. If the 

 ventricles are cut across it is 

 at once apparent that the left 

 ventricle has the heavier walls. 

 The cavity of the right ven- 

 tricle in such a section is cres- 

 centic and it seems an appen- 

 dage upon the left. (Fig. 53.) 

 The heart is supported by 

 the clustered vessels and ad- 

 jacent structures. The ar- 

 teries and veins may be re- 

 called: there is the aorta, 

 arching up from the left ven- 

 tricle, the short pulmonary 

 artery rising from the right 

 ventricle and forking under 

 the arch of the aorta, the two 

 venae cavae connecting with 

 the right auricle, and the four 

 pulmonary veins entering the 

 left auricle. There is a well- 

 marked groove between the 

 auricles above and the ventri- 

 cles below. The auricles have uneven contours while the 

 ventricles are smooth. 



The cavities of the heart are lined by an epithelium 

 like that of the capillaries. Between this and the 

 pericardium the essential tissue is muscle of the unique 

 order which we call cardiac. The cells are short cylinders 

 united end to end in bundles. The strands which result 

 have a most intricate arrangement; in general it may be 



FIG. 53. A general view of 

 the heart, the ventricles being 

 cut across to show the crescen- 

 tic form of the right, appearing 

 like an appendage upon the left. 



