702 



HUMAN ANATOMY. 



Left 

 auriculo- 

 ventricular 

 orifice 



Tendon of 

 conus arteriosus 



Right auriculo- 

 ventricular orifice 



Septal papil- 

 lary muscles 



Posterior 

 papillary 

 muscles 



ventricles, and when they reach the apex, they bend upon themselves and pass 

 deeply and upward to terminate in the papillary muscles of the left ventricle. Those 

 fibres which arise from the left auriculo-ventricular fibrous ring cross the posterior in- 

 terventricular groove and, pass- 

 ^'*^- ^^5 ing beneath the fibres from the 



right ring, encircle the right ven- 

 tricle and finally terminate in the 

 papillary muscles of that ven- 

 tricle. 



On the removal of these 

 superficial fibres a deeper set is 

 seen, which seem to form two 

 muscular cones, each surround- 

 ing one of the ventricles. In 

 the adult heart it is difficult to 

 perceive the true relations of the 

 two cones, but in the hearts of 

 young individuals up to two or 

 three years of age it has been 



Diagram of course of superficial muscle layers originating in anterior f^,,,,^ fl-iaf KntVi tVi^ nnnpc Qrf» 

 half of tendon of conus arteriosus. (MarCallum.) lOUUG tuac DOin tne COneS are 



formed by the curving of a con- 

 tinuous sheet of fibres in an S-shaped manner. This deep sheet of fibres takes its 

 origin principally from the right auriculo-ventricular fibrous ring and from the ten- 

 dinous band of the conus arteriosus, and encircles the right ventricle, lying beneath 

 the superficial layer. When it reaches the posterior border of the ventricular sep- 

 tum, it passes forward in that structure, and then encircles the left ventricle, termi- 

 nating finally in the papillary muscles of that ventricle. The deep fibres which arise 

 from the left fibrous ring are entirely confined to the left ventricle, forming a circular 

 band surrounding its basal portion. 



Structure. — The heart muscle, the myocardium, is both covered and lined 

 with serous membrane, the epicardhmi, as the visceral layer of the pericardium is 

 often called, investing it externally and the endocardium, continuous with the intima 

 of the large blood-vessels, clothing all parts of its elaborately modelled inner surface. 



The epicardium corresponds in its general structure with other parts of the 

 pericardium, consisting, as do other serous membranes, of a single layer of endothelial 

 cells that covers its free surface and rests upon a stratum of fibro-elastic connective 

 tissue. The elastic fibrillae are very fine and numerous and, immediately beneath the 

 endothelium, form a dense net-work. When not separated from the muscle by 

 subserous fat, as it con- 

 spicuously is in the in- Fig. 666. 

 terventricular and auric- 

 ulo-ventricular grooves, 

 the epicardium is inti- 

 mately attached to the 

 subjacent muscular tis- 

 sue. The numerous 

 branches of the coron- 

 ary vessels, as well as 

 the nerve trunks and 

 the microscopic ganglia 

 connected with the car- 

 diac plexuses, lie be- 

 neath the epicardium or 

 within its deepest layer. 



The endocardium 

 follows all the irregular- 

 ities of the interior of the heart, lining every recess and covering the free surfaces of 

 the valves, tendinous cords and papillary muscles. It consists of the endothelium 

 and the underlying connective tissue. The latter is differentiated by the distribution 



Endo 

 thelium 



Layer rich 

 in elastica 



Deepest 

 layer 







Heart muscle 



Blood-vessel 



Section of endocardium 



