THE HEART. 469 



there are varieties in the arrangement due to individual differences. If the 

 I'picardium and the subjacent fat are removed from a heart which has been subjected 

 to prolonged boiling, so as to dissolve the connective tissues, the superficial fibres 

 of the ventricles will be exposed. They will be seen to commence at the base of 

 the heart, where they are attached to the tendinous rings around the orifices, and 

 to pass obliquely downward toward the apex, with a direction from right to left. 

 At the apex the fibres turn suddenly inward into the interior of the ventricle, 

 forming what is called the vortex. On the back of the heart it will be seen that 

 the fibres pass continuously from one ventricle to the other over the interventricular 

 groove ; and the same thing will be noticed on the front of the heart at the upper 

 and lower end of the anterior interventricular groove, but in the middle portion 

 of this groove the fibres passing from one ventricle to the other are interrupted 

 by fibres emerging from the septum along the groove ; many of the superficial 

 fibres pass in also at this groove to the septum. The vortex is produced, as stated 

 above, by the sudden turning inward of the superficial fibres in a peculiar spiral 

 manner into the interior of the ventricle. Those fibres which descended on the 

 posterior surface of the heart enter the left ventricle at the vortex, and, ascending, 

 form the posterior part of the inner layer of muscular fibres lining this cavity and 

 the right (posterior) musculus papillaris ; those fibres which descend on the front 

 of the heart to reach the apex also pass, at the vortex, into the interior of the 

 ventricle, where they form the remainder of the innermost layer of the ventricle 

 and the left (anterior) musculus papillaris. The fibres forming the inner layer of 

 the wall of the ventricle ascend to be attached to the fibrous rings around the 

 orifices. 



By dissection these superficial fibres may be removed as a thin stratum, and it 

 will then be found that the ventricles are made up of oblique fibres superimposed in 

 layers one on the top of another, and assuming gradually a less oblique direction as 

 they pass to the middle of the thickness of the ventricular wall, so that in the centre 

 of the wall the fibres are transverse. Internal to this central transverse layer the 

 fibres become oblique again, but in the opposite direction to the external ones. This 

 division into distinct layers is, however, to a great extent artificial, as the fibres 

 pass across from one layer to another, and have therefore to be divided in the 

 dissection, and the change in the direction of the fibres is very gradual. These 

 oblique fibres commence above at the fibrous rings at the base of the heart, and, 

 descending toward the apex, they enter the septum near its lower end. In the 

 septum the fibres which form the left ventricle may be traced in three directions : 

 1. Some pass upward to be attached to the central mass of fibrous tissue. 2. Others 

 pass through the septum to become continuous with the fibres of the right ventricle. 

 3. The remainder pass through the septum to encircle the ventricle as annular 

 fibres. Of the fibres of the right ventricle, some on entering the septum pass 

 upward to be attached to the central mass of fibrous tissue ; some, entering the 

 septum from behind, pass forward to become continuous with the fibres on the 

 anterior surface of the left ventricle ; and others, entering in front, pass backward 

 to join the fibres on the posterior wall of the left ventricle. The septum therefore 

 consists of three varieties of fibres viz., annular fibres, special to the left ventricle ; 

 ascending fibres, derived from both ventricles and ascending through the septum 

 to the central fibro-cartilage ; and decussating fibres, derived from the anterior wall 

 of one ventricle and passing to the posterior wall of the other ventricle, or from 

 the posterior wall of the right ventricle and passing to the anterior wall of the left. 

 In addition to these fibres there are a considerable number which appear to encircle 

 both ventricles and which pass across the septum without turning into it. 



Vessels and Nerves. The arteries supplying the heart are the right and left 

 coronary from the aorta. 



The veins accompany the arteries, and terminate in the right auricle. They are, 

 the anterior or great, posterior, left and anterior cardiac veins, the right or small, 

 and the left or great, coronai'y sinuses and the venae Thebesii (vence cordis minimce). 



The lymphatics terminate in the thoracic and right lymphatic ducts. 



