THE HEART. 1095 



heart is said to be composed are not independent, but their fibres are interlaced 

 to a considerable extent, and therefore any separation into layers must be to 

 a great extent artificial : and also no doubt partly due to the fact, pointed out by 

 Henle, that there are varieties in the arrangement due to individual differences. 

 If the epi'-'ardiuni (visceral layer of pericardium) and the subjacent fat is 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 in- 

 ward, forming what is called the vortex, into the interior of the left ventricle. 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 left 

 ventricle. Those fibres which descended on the posterior surface of the heart 

 enter, at the vortex, the left ventricle, and, ascending, form 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, and which pass to the apex, 

 also pass, at the vortex, into the interior of the ventricle, where they also 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 lu-n-s 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 fibro-cartilage. 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 fibro-cartilage ; 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 left or anterior 

 and right or posterior coronary (page 542). 



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



