THE HEART. 



509 



Fig. 263. 



heart belongs to the system of organic life, as it contracts without the 

 participation of the will. Nevertheless, it is formed of red striated fibres 

 which only differ from the muscular fibres of animal life in being less in 

 diameter. As in the tongue, these fibres also possess ramifications that unite 

 them to each other; they are likewise very granular. (They are more 

 friable than those of the muscular system generally; the sarcolemma is 

 more delicate, and the longitudinal markings and nuclei are more apparent 

 the latter being placed in the axis of the fibre along with rows of minute 

 fatty granules, which are extremely numerous in fatty degeneration of the 

 heart. The connective tissue is scanty ; so that the fibres lie closer together 

 while forming innumerable anastomosing networks and interlncin't's— a 

 character peculiar to the muscular organisation of the heart. It has°been 

 asserted that there is no sarcolemma.) 



The striation of the muscular fibres of the heart, 

 •which constitutes an exception in the laws of organisa- 

 tion, may be explained to a certain point by the nature 

 of the functions imposed on the muscular tissue of the 

 organ. Charged to propel the blood into the arterial 

 ramifications by successive, instantaneous, and vigorous 

 contractions, the heart, probably, would not have been 

 capable of executing such movements if it had been com- 

 posed of organic fibres, as these come into action in a 

 steady, slow, and prolonged manner. The ramifications 

 that unite the fibres, and establish a kind of solidarity 

 between them, afford a clue to the simultaneousness in 

 the movements of the auricles and ventricles. 



It is also worthy of remark, that between these 

 fibres there is so little connective tissue that the majority 

 of anatomists absolutely deny its existence. 



The arrangement of the muscular fasciculi of the 

 heart has been the object of numerous recent investigations, which have 

 only complicated what was already known on the subject. "We will endea- 

 vour to sum up, as simply as possible, this arrangement, in examining it in 

 the different compartments of the organ. The following is the disposition 

 of the fasciculi, considered successively in the ventricles and auricles : 



1. FiBEES OF THE Vbnteicles. — According to the remark of Winslow, 

 we may compare the ventricles, in regard to the arrangement of the fibres 

 essentially composing them, to " two muscular sacs included in a third :" 

 that is to say, each ventricle is formed of proper muscular fibres, covered 

 externally by a layer of unitive fibres, which envelop the two ventricles in 

 common. 



a. Proper fibres of the ventricles. — Taken altogether, these fibres repre- 

 sent, for each cavity, a hollow cone, open at both its extremities : at the 

 superior extremity, by the auriculo- ventricular and arterial orifices ; and at the 

 inferior extremity, by an aperture which admits the reflected fibres of the 

 common layer. All form loops attached, by their extremities, to the out- 

 line of the superior orifices, on the fibrous zones, and are rolled, more or 

 less obliquely, around the axis of the ventricles. It is from the apposition 

 of the right and left systems that the ventricular septum is formed. 



6. Unitive fibres of the ventricles. — These are disposed as an external 

 shell enveloping the proper fibres. They leave the fibrous zones at the base 

 of the heart, and descend towards its apex : those of the right side, by inclining 

 forward ; the anterior, in following the direction of the great axis of the 



ANASTOMOSING MUS- 

 CDLAR FIBEES OF 

 HEART. 



