320 



THE HEART. 



left of the heart, pass in part across the anterior longitudinal groove, covering partially 

 the coronary vessels, and in part dip into the groove and ascend obliquely upon the 

 right side of the septum. The anterior fibres of the left ventricle are derived in part 

 from those arising from the roots of the great vessels, in part from those crossing the 

 coronary groove from the right, and in part they come out from the left surface of the 

 septum, into which they dip in front like those of the right ventricle ; those of the 

 anterior fibres of the left ventricle which are near the apex pass spirally round this 

 part to enter the whorl posteriorly, while the posterior set of superficial fibres, turning 

 round the apex with a similar spiral, arrive in front and there enter the vortex. 

 These fibres thus carried into the interior ascend upon the posterior and anterior 



Fig. 239. 



Fig. 239. VIEW OF THE FIBRES OF 

 THE SHEEP'S HEART, DISSECTED AT 



THE APEX TO SHOW THE " VoilTEX " 

 IN WHICH THE FIBRES ENTER THE 

 APEX IN TWO SETS FROM THE Ex- 



TERNAL LAYER (from Pettigrew). 



a, a, anterior fibres entering the 

 apex of the left ventricle posteriorly 

 at Z; c, c, posterior fibres entering 

 the apex anteriorly at d. 



internal surfaces of the left ven- 

 tricle, forming the almost longi- 

 tudinal innermost layer of fibres, 

 and contribute to form the columnse carnece and musculi papillares. Their direction, 

 as they ascend internally, is nearly the opposite of that in which they made their 

 descent externally. 



The direction of the fibres in the successive layers gradually changes as we proceed 

 from without inwards ; for example, on the front of the right or left ventricle it is 

 at first very oblique from right to left of the heart, or indeed in some parts almost 

 longitudinal from base to apex,* it then becomes less and less oblique, until in the 

 middle layer, which is also the thickest, it is transverse ; the obliquity being now 

 resumed and gradually increasing, the direction is changed to that from right to left 

 of the heart and from apex to base upwards, until at last in the interior it is extremely 

 oblique, or nearly longitudinal. 



Fig. 240. 



Fig. 240. DISSECTION OF THE VEN- 

 TRICLES OF THE SHEEP'S HEART, 



VIEWED FROM BEHIND, A PART OF THE 



POSTERIOR WALL BEING REMOVED TO 

 snow A DISSECTION OF THE FIBRES OF 

 THE SEPTUM AT A SIMILAR DEPTH 

 (from Pettigrew). | 



a, the superficial layer of fibres of the 

 right ventricle ; b, the same of the left 

 ventricle at the base arid apex pos- 

 teriorly ; a 4 , the fourth or middle layer 

 of fibres of the right ventricle exposed ; 

 Z> 4 , the same layer of the left ventricle ; 

 c 4 , the same of the septum, showing the 

 fibres of that layer continued forward 

 from those of the left ventricle. 



It is only the three outer layers and part of the fourth layer which are distributed 

 round both ventricles ; the three internal layers belong solely to each ventricle. 



The septum consists of three sets of fibres, viz., 1, those belonging to the right 

 ventricle : 2, those belonging to the left ; and 3, those common to both ventricles. 



The difference of thickness of the walls of the right and left ventricles, which is so 



The direction is less longitudinal in the human heart than in that of the sheep. 



