FIBRES OF THE HEART. 



621 



them within their proper spheres of action, 

 and since the fibres of the heart are devoid of 

 this agent, the question arises as to what other 

 retaining power these possess. On this head 

 no difficulty presents itself; for the fibres, in 

 winding round and round the cavity of the left 

 ventricle, become arranged in concentric layers ; 

 and in taking a larger sweep, in surrounding 

 the right ventricle, the same arrangement is 

 preserved, so that during the systole of the 

 heart the whole mass of the fibres firmly com- 

 press each other, which necessarily retains them 

 all within their proper spheres of action, ex- 

 cepting the superficial fibres, of which those 

 towards the base, and especially those upon the 

 right ventricle, where there is great latitude of 

 motion, do not, preserve a parallelism with their 

 subjacent fibres, but lie nearly at right angles 

 with them. It is on this account, most proba- 

 bly, that the superficial fibres have attracted 

 notice, and have been viewed as a distinct 

 layer. 



The disposition of the fibres varies in diffe- 

 rent parts of the heart, forming parallel lines, 

 angles, decussations, flat and spiral twists. The 

 fibres are arranged in fasciculi, bands, layers, 

 and a rope, which are so entwined together as 

 to form the two chambers called the right and 

 left ventricles. These are lined with their in- 

 ternal proper membrane. 



The fasciculi are connected with the aorta, 

 pulmonary artery, and carneae columnae, and 

 contribute to the formation of the bands. 



The bands. By tracing the fibres in bands, 

 we are enabled to develop the formation of the 

 ventricles in a progressive and systematic man- 

 ner. The bands spring from a mass of fibres 

 which forms the apicial part of the left ventricle, 

 and which, in winding round just above the 

 apex of the heart, separates into two bands to 

 form the right ventricle. 



It will render the demonstration more intel- 

 ligible if a preliminary and cursory view be 

 taken of the general course of these bands 

 (Jig- 283, p. 626,) by referring to the diagram. 

 The bands, as there given, form a mere 

 skeleton of the heart, merely indicating the se- 

 veral courses they take. The average width of 

 the bands is not less than a third of the extent 

 between the apex and base of the left ventricle. 

 In the diagram, cue indicates the winding of 

 a considerable mass of fibres just above the 

 apex ; at the septum, s, it splits into two bands. 

 The shorter, CACC, encircles spirally both 

 ventricles, one half round the right, the other 

 round the left ventricle. The longer band de- 

 scribes two circles : it first passes through 

 the septum, round the left ventricle marked 

 CPCA ; it secondly passes round the base, and 

 includes both ventricles in its circuit, marked 

 progressively CPCAA,CPCAAA, CPCAAAAC, and 

 RR. 



After employing so many letters, it is requi- 

 site to explain that as the bands are frequently 

 receiving fresh accessions of fibres, it is desira- 

 ble to characterise those increments individually 

 by the initials of the names of the respective 

 sources from which they are derived ; and in 

 order to make a distinction between the indica- 



tions of the fibres and of their respective origins, 

 the latter are characterised by double, and the 

 former by single initials. Accordingly, the 

 aorta, the pulmonary artery, the rope, and the 

 carneae columnae are designated AA, PP, RR, 

 and cc, while their fibres are marked A, p, R, 

 and c. This plan is modified in one instance 

 only, viz., the fibres of the main bulk of the 

 heart, being derived from the rope and the two 

 carneae columnae of the left ventricle, are desig- 

 nated in the first instance by their proper ini- 

 tials CRC ; but as numerous increments of 

 fibres are being made, in succession, to these 

 three original sets, it is convenient to make an 

 abbreviation in the lettering ; thus, CRC is in- 

 dicated by C large, when combined with 

 other initials; accordingly, CRCA is con- 

 tracted to CA, and CRCPCA to CPCA, and so 

 with the rest. 



The layers. Although the heart admits of 

 being split into a number of layers, yet there 

 being no material division formed by fasciae or 

 condensed cellular membrane, such separations 

 are strictly arbitrary. It is, however, found 

 convenient to separate the fibres into certain 

 layers, in order to give a methodical de- 

 monstration of the formation of this organ. 

 The same remarks obtain regarding the bands. 



It is generally supposed that the superficial 

 fibres properly constitute a distinct layer, form- 

 ing a common sac, which encloses the two 

 ventricles. This is not strictly the case, for it 

 has the same origins and terminations as have the 

 fibres immediately subjacent to it. Neverthe- 

 less, the superficial fibres are, in the following 

 description, considered as a separate layer, to 

 show the peculiar construction of the apex. 



The rope. It has already been stated that 

 the longer of the two bands terminates at the 

 base in the rope. The fibres of this band, in 

 forming the brim of the left ventricle, make a 

 sharp twist like those of a rope, by which 

 means they become the inner fibres of this 

 chamber, and expand into a layer which enters 

 largely into the formation of the mass which 

 divides into the two bands. So the principal 

 band, although it receives several increments of 

 fibres, has no complete beginning nor ending, 

 a considerable portion of it originating and ter- 

 minating in itself, which circumstance renders 

 it necessary to fix upon the most convenient 

 part of its course for the commencement of the 

 demonstration. 



Although the system here adopted of unra- 

 velling the fibres of the heart be strictly arbi- 

 trary, as every other must be, yet it will, most 

 probably, be found the only method by which 

 all the various courses, and several connexions 

 made by the fibres in forming the heart, could 

 be displayed. 



The demonstration. It is requisite to pur- 

 sue two methods of demonstration ; one, de- 

 scribing the dissection, or unfolding, which 

 consists in unravelling and separating the fibres, 

 and tracing, from the circumference to the cen- 

 tre of the heart, their various courses, in the 

 form of bands, by which they become in order 

 unwound, and by which a general view of the 

 formation of the two ventricles is at the 



