ARRANGEMENT OF THE MUSCULAR FIBRES. 



869 



veins on the left side of the heart (g, h), the muscular fibres extending for some 

 distance from the auricle upon the veins, especially upon the superior vena cava 

 and the pulmonary veins. The fossa ovalis in the septum is also encircled by 

 annular fibres. 



Fibres of the ventricles. The muscular fasciculi of the ventricles have a 

 very intricate disposition, which has received great attention from anatomists. 

 Many of the statements, however, are conflicting, and it must be confessed that the 

 subject still requires farther investigation. 1 



The fibres on the outer surface of the ventricles (figs. 319, 32 ()*_#,_ J) extend 

 from the base, where they are attached to the tendinous structures around the 

 orifices, towards the apex of the heart, where they pass with an abrupt twist into 

 the interior of the left ventricle. Their general direction is not vertical but oblique, 

 especially in front (fig. 319), just as if while the base of the organ remained fixed 

 the apex had been twisted half round in the direction of the motion of the hands 



Fig. 321. SURFACE FIBRES OF THE VEN- 

 TRICLES OF THE HUMAN HEART FROM 

 THE FRONT AND BELOW. (Reid.) 



b, bundle of fibres emerging from the 

 interior of the left ventricle at the vortex 

 a, and crossing the lower part of the 

 septum uninterruptedly. At d, the sur- 

 face fibres are somewhat interrupted. 



of a watch. They form a dis- 

 tinct thin superficial stratum, 

 best marked at the back of the 

 right ventricle, for here the 

 direction of the fibres is quite 

 different from those immediately 

 beneath. At the back they pass 

 over the septum without turning 

 in : at the front they are some- 

 what interrupted by fibres which 

 come out from the septum ; 



except towards the base and apex, where they cross uninterruptedly from one 

 ventricle to the other (fig. 321). 



If the superficial fibres are traced into the interior of the left ventricle at 

 the apex, it is found that they pass for the most part into continuity with the 

 papillary muscles, and the adjacent parts of the inner layer of muscular fibres of 

 that cavity. Most of those which are seen crossing over the front and left side 

 of the heart can be traced towards the posterior papillary muscle, whilst those 

 which pass over the back and right side of the heart, are chiefly continuous with the 

 anterior papillary muscle. Many of the superficial fibres, however, after gaining 

 the interior of the left ventricle, do not pass into the papillary muscles, but spread 

 out as an inner vertical layer of muscular fasciculi, which pass upwards to be 

 attached to the fibrous rings at the base of the ventricle. 



The peculiar spiral concentration of the fibres of the heart at the apex is known as 

 the vortex or whorlf&nd is produced, as already described, by the twisting or inter- 

 locking of the external fibres as they pass to be continuous with those in the interior. 



1 For convenience of description in the following account of the course of the fibres, the heart is 

 supposed placed apex downwards, and with the anterior and posterior surfaces about equally occupied by 

 the two ventricles (as represented in figs. 319, 320). 



