626 



FIBRES OF THE HEART. 



portion 2 is seen crossing over to join the band 

 CPCAAAAC, just before it becomes the rope ; 

 the fasciculus of fibres A from the aorta A A 

 is also seen joining this band at its inner sur- 

 face nearer the base. By the union of these 

 two fasciculi with the band in question, the 

 basial half of the posterior boundary of the 

 right ventricle is formed. By pursuing, in 

 jig. 282, this band or combination of fibres, 

 'lettered CPCAAAAC, it is seen to form, while 

 it is gradually twisting upon itself, the brim 

 of the left ventricle, and then to make a 

 sharp twist of its fibres into the rope R R, by 

 which means they are rendered the internal 

 fibres of the left ventricle ; in Jig. 280 they 

 may be traced expanding again into a layer, 

 pursuing the same spiral sweep from left to 

 right, but from the base towards the apex, and 

 inwardly instead of outwardly. Thus the de- 

 monstration brings us back to our starting-point. 



We have yet to trace the shorter of the two 

 bands which originate in the splitting of the 

 middle mass of fibres, CRC, in fig. 278, to 

 embrace the right ventricle. This view ex- 

 hibits only the inner fibres of this mass as they 

 are prolonged into the inner or longer of the 

 two bands; but fig. 281 affords an outer view 

 of this mass of fibres as they are prolonged 

 into the outer or shorter band. They are seen 

 winding spirally up from the apex marked 

 CRC, and at the anterior coronary track, act, 

 they split, in the form of a band, from the 

 general mass to pass over the lower half of the 

 cavity of the right ventricle. In this figure 

 this band is separated and left extended, in 

 order that the accessions of fibres it receives 

 from the right surface of the septum may be 

 seen, which are the fibres A from the aorta 

 A A, and the fibres c and c form two of the 

 carneae columnse (not in view) passing obliquely 

 down from right to left to the anterior edge of 

 the septum, from which they extend into the 

 band which is lettered CACC, and unite in- 

 timately with its fibres. When the band is 

 replaced in its course over the ventricle, its 

 accessory fibres are made to reflect at an acute 

 angle upon themselves, and thus form the 

 apicial part of its anterior boundary. This 

 band describes one spiral circle round the heart, 

 arriving again at the anterior coronary track at 

 its basial extremity; it is inserted into the 

 aorta, and if the fibres make a very oblique 

 approach to the base, they will be also inserted 

 into the tendinous margin of the annulus arte- 

 riosus. The continuation of this band round 

 the posterior side of the heart can be traced in 

 Jig. 279. Its width is equal to about a third 

 of the heart's axis; it is seen marked CACC 

 in its spiral ascent from left to right, passing, 

 first,a little below the middle third of the heart; 

 at the posterior coronary track, pet, becom- 

 ing the middle third, and afterwards approach- 

 ing gradually the base in its way to its points 

 of insertion before-mentioned. 



As the tracing the fibres from the circum- 

 ference to the centre, and from the centre to 

 the circumference, is a matter of much difficulty, 

 and as the description has been attended with 

 much detail, it is desirable that a more general 



and concise view by means of a diagram should 

 be afforded of the courses which the fibres take 

 in constructing this organ. 



RECAPITULATION. (Vid.thediagram/g.283.) 

 We commence tracing the fibres of the heart 

 from its very centre. The fibres, cc, from the two 

 carnese columnae of the left ventricle, LV, are 

 joined by the fibres, R, from the rope RR, 

 after those fibres of the rope have expanded 

 and formed the internal layer of the septum S ; 

 in winding round the axis of this cavity they 

 blend together as the initial letters CRC indi- 

 cate. The inmost of these fibres descend as far 

 as the apex, where they twist sharply round and 

 close the cavity, by which means they construct 

 the apex, and become the superficial fibres of 

 the heart. But the chief bulk of this mass of 

 blended fibres makes a spiral sweep from left 

 to right round the axis above the apex ; and when 

 it has described two circles, CRC, it splits at 

 the anterior edge of the septum into two bands, 

 one being considerably longer than the other. 

 The longer first makes one circle round the left 

 ventricle, then another, enclosing both ventri- 

 cles. In making the first circle it passes 

 through the septum forming its middle layer, 

 and on reaching its posterior edge itreceives from 

 the pulmonary artery accessory fibres, which 

 have crossed over the cavity of the right ven- 

 tricle, forming the inmost layer of its right or 

 proper wall, and fibres from one of the carnese 

 columnae of this ventricle, and from the aorta, 

 being marked CPCA. The accessory fibres 

 are not represented, as they would have ren- 

 dered the diagram complicated and unintelligi- 

 ble ; but they are indicated by their initials 

 being added in the lettering of the bands. 

 This band in question may now be traced 

 round the middle third of the left ventricle 

 advancing towards both the base and the outer 

 surface of the heart; on completing its first 



Fig. 283. 



