342 



PRACTICAL ANATOMY. 



The endocardium is the serous lining of the heart 

 and is continuous with the inner coat of the great vessels. 

 It is considerably modified where it enters into the forma- 

 tion of the valves, being in these situations re-inforced by 

 bundles of fibrous tissue and some muscular fibres. It 

 lines the interior of the ventricle, columnse carneee, and 

 chordae tendinese. 



The structure of the heart consists of planes of mus- 



FIG. 147. COURSE OF THE MUSCULAR FIBRES OF THE HEART. 



A, on the anterior surface ; B, view of the apex with the vortex : C, course of the fibres 

 within the ventricular wall ; D, fibres passing into a papillary muscle. 



cular fibres arranged so as to effectually empty the 

 cavities of the heart and exert sufficient force to drive 

 the blood through all parts of the vascular system. 

 These planes of muscular fibres arise from the fibrous 

 rings at the base surrounding the auriculo-ventricular, 

 pulmonary, and aortic orifices. They are divisible into 

 three principal layers : the oblique, transverse, and spiral. 

 The transverse layer is thick and strong and encircles the 



