318 



THE HEART. 



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

 the pulmonary veins. 



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

 very intricate disposition, which has received great attention from various 

 anatomists, such as Wolff, Gerdy, Reid, Searle, and most recently Pettigrew, 

 the last of whom has done much to elucidate the nature of the arrangement 

 in animals, although perhaps the whole subject cannot yet be considered as 

 fully understood. 



Fig. 237. Fig. 237. POSTERIOR VIEW OP 



THE SAME PREPARATION AS 

 IS REPRESENTED IN THE PRE- 

 CEDING FIGURE. | 



a, posterior surface of the 

 right ventricle with its super- 

 ficial muscular fibres dissected ; 



b, the same of the left ventricle ; 



c, posterior interventricular 

 groove, from which the coronary 

 vessels have been removed ; d, 

 right auricle ; e, the left, 

 showing some transverse fibres 

 common to both auricles, and 

 some belonging to each one ; /, 

 superior vena cava ; g, g f , pul- 

 monary veins cut short; h, 

 sinus of the great coronary 

 vein covered by muscular fibres ; 

 h', posterior coronary vein join- 

 ing the principal one ; i, inferior 

 vena cava ; i', Eustochian valve 

 as seen from behind. 



It is chiefly the reticu- 

 lated structure or continual 

 union of the greater part 

 of the muscular fibres with 

 each other which renders 

 difficult the investigation 



of the course and disposition of these fibres. In order to unravel them 

 with any degree of success, it is best to boil the slightly distended 

 heart for five or six hours, so as to destroy the connective tissue, and then 

 carefully to dissect the heart in part by cutting and in part by tearing 

 asunder the fibres with blunt instruments. 



According to Pettigrew's observation?, made principally upon the hearts of rumi- 

 nating animals, as many as seven layers of fibres may be distinguished in the walls of 

 both ventricles ; * three of these being external, three internal, and one situated inter- 

 mediately between them : but it may be remarked that, although some of these 

 layers, such as the external, may be readily separated from the next, others of them 

 run so much into those with which they are in contact, that we must regard the dis- 

 tinction of layers as applying more strictly to the difference of the direction of the 

 majority of the fibres at different depths, than to a real and constant separation of 

 determinate layers, in each of which the fibres are alike in direction. At the same 

 time, for the convenience of description, it may be well to recognise provisionally the 

 seven layers of Pettigrew. 



One of the most important facts which have been established by Pettigrew's 



Wolff conceived that five or six layers might be made out. 



