MUSCULAR STRUCTURE VENTRICLES. 



319 



researches, is that of the continuity of the fibres of certain external layers with those 

 of corresponding internal layers. This continuity takes place at the base of the heart 

 round the auriculo-ventricular orifices and upon the septum, and at the apex of the 

 left ventricle in that peculiar spiral concentration of the fibres known to previous 

 observers as the vortex or whorl. Thus the fibres of the first or external layer are 

 continuous with those of the deepest or innermost, in part by folding over the margin 

 of the auriculo-ventricular orifice, and in part by penetration through the apex. In 

 the same manner the fibres of a second or deeper external layer are continuous with 

 those of a layer named the sixth by Pettigrew, and the fibres of the third external 

 layer with those of the fifth ; while the fibres of the middle or fourth layer of Petti- 

 grew may be considered to return upon those of the same set. In this manner the 

 first and seventh layers enclose all the others, the second and sixth enclose those 

 within them, and the third and fifth enclose the fourth. 



The fibres of the ventricles, therefore, do not take their origin, as was in general 

 previously held, from the fibrous rings surrounding the auriculo-ventricular orifices 



Fig. 238. 



Fig. 238. VIE\V OP A PARTIAL DISSEC- 

 TION OP THE LAYERS OP FIBRES OP 

 THE VENTRICLES IN A SHEEP'S HEART 

 IN FRONT (after the manner of Pet- 

 tigrew). | 



At the base and apex the pericardium 

 and connective tissue and fat alone have 

 been removed, and the superficial layer 

 of fibres is displayed on these parts of 

 both ventricles. In the intervening 

 space, layer after layer of the fibres has 

 been removed from above downwards, 

 reaching to a greater depth on the left 

 than on the right side, a 1 , a 1 , the 

 superficial layer of the right ven- 

 tricle ; b\ ft 1 , the same of the left 

 ventricle ; 2, the second layer of both 

 ventricles ; 3, the third ; 4, the fourth or 

 central, with fibres nearly transverse; 5 

 and 6, two of the deeper layers coming 

 next ; and 7, a small part of the fibres 

 of the deepest layer on the front of the 

 left ventricle, passing into one of the 

 larger papillary muscles, and derived 

 from the posterior superficial fibres, which 

 have entered the whorl of the apex ante- 

 riorly ; the different degree of obliquity 

 and other changes of direction of the 



fibres is shown in these several layers ; c, c, between these letters and numbers is the 

 anterior coronary or interventricular groove, in which superiorly the greater part of the 

 fibres of the superficial layer is seen to cross from right to left ; in the remaining part of 

 the groove, which is dissected, part of the fibres from both ventricles is seen to turn 

 backwards towards the septum ; d t the pulmonary artery cut short ; e, the first part of 

 the aorta. 



and the roots of the great arteries. The only fibres which come in contact with 

 those structures are the fibres of the superficial layer, where they dip in to be con- 

 tinuous with those of the deepest layer ; and even these for the most part exhibit, on 

 careful dissection, no breach of continuity of muscular fibres, but are merely bound 

 down by white tissue penetrating between the fasciculi ; a small portion, however, of 

 the muscular fibres which surround the auriculo-ventricular orifices become continuous 

 with the segments of the valves and with chordae tendineae, and through them with 

 the musculi papillares, the fibres of which belong chiefly to the innermost layer. 



Some fibres, especially those belonging to the superficial layers, and more especially 

 upon the posterior surface of the heart, pass round and enclose both ventricles ; others, 

 especially in front, may be considered to belong to one ventricle only. Thus the 

 anterior superficial fibres of the right ventricle, in descending from the right to the 



