624 



FIBRES OF THE HEART. 



the base, pass more longitudinally. It is evi- 

 dent that these few fibres would be inadequate 

 to form a complete layer, unless in their pro- 

 longation they pursued an uniformly spiral 

 course. They are more than enough to cover 

 the apicial part as they twist over each other; 

 but in consequence of the conical form of the 

 heart they soon become singly arranged, and 

 as they diverge, separate and leave interspaces, 

 some of which are occupied by fibres which 

 apparently arise abruptly at the surface. The 

 fibres which pass longitudinally to the base of 

 the left ventricle are inserted into the tendinous 

 margin of the annulus arteriosus, and into the 

 posterior part of the root of the aorta, forming 

 the right wing, cue. The spiral fibres have 

 been stated to arrive at the anterior coronary 

 track along its whole length. The majority of 

 them terminate at the coronary vessels ; others 

 are merely intersected by them, while others 

 pass under these vessels and become super- 

 ficial again : those which maintain their course 

 over the right ventricle vary in different hearts 

 from a small to a considerable number. Along 

 the whole length of this track accessory fibres 

 from the interior of the right ventricle are 

 emerging to associate with these in their way 

 over this ventricle. They take a longitudinal 

 course to the base, and therefore start at an 

 angle with the spiral fibres which are on the 

 left side of the coronary track. In Jig. 281 

 these accessory fibres from the aorta, A A, and 

 from two of the carneae columns?, are seen 

 passing together obliquely down the right sur- 

 face of the septum, marked ACC, to enter 

 into the formation of the extended band. 

 These accessory fibres perforate it along the 

 anterior boundary, ab, and become super- 

 ficial. This layer is, accordingly, in Jig. 279, 

 marked CACC; its fibres pass at nearly right 

 angles with the subjacent fibres, and when 

 raised form the left wing; its insertions are 

 the anterior part of the root of the aorta, the 

 tendinous margin of the annulus venosus, and 

 again the right part of the root of the aorta. 

 Sometimes festoons are formed at the base by 

 communications of fibres between the pulmo- 

 nary artery and the aorta, at its right and pos- 

 terior aspects. 



It occasionally happens that the accessory 

 fibres which arise from the interior of the right 

 ventricle are not very numerous; in such cases 

 a greater number of fibres arise abruptly from 

 its surface. 



The superficial layer has three sets of ori- 

 gins : one, primitive, from the interior of the 

 left ventricle; the others, accessory, from the 

 interior of the right ventricle, and from the 

 outer surface of both. It cannot with pro- 

 priety be considered as one common invest- 

 ment, since each ventricle for the most part 

 gives birth to its own superficial fibres. It is 

 necessary to raise it as a distinct layer for two 

 reasons : first, that the superficial fibres of 

 the right ventricle in general pass nearly at right 

 angles with their subjacent fibres, and there- 

 fore require to be removed in order to proceed 

 with the next stage of separation : secondly, 

 that it developes the peculiar mode of closing 



the left ventricle, and of forming the apex; 

 and probably no other method than that of the 

 twisting of the fibres could have been so secure, 

 especially as the parietes at the apex of the 

 ventricle do not generally, even in a bullock's 

 heart, exceed a tenth of an inch in thickness. 



The second stage The external layer having 

 been traced from its origins to its insertions, 

 we may now trace the deep-seated layers ; and 

 as these have, for the most part, the same 

 origins, courses, and insertions as the super- 

 ficial layer, we may commence the description 

 at the same points. 



It has been already stated that the fibres of 

 the rope and of the two earner columnae ex- 

 pand in a fan-like manner, that their inmost 

 fibres pass through the apex and become ex- 

 ternal, but that the chief of them wind round 

 the axis of the left ventricle above the apex, 

 as exemplified in fig. 279, cue. The respec- 

 tive sets of fibres pertaining to these three 

 bodies continue separate during their radiation 

 only, after which they become plaited together 

 by folding one over the others. Their mode 

 of association is shown in the extended portion 

 of the split layer, cue in fig. 280, also in 

 its counterpart, CRC, winding round the api- 

 cial part of the ventricle. Again, in fig. 278, 

 it may be seen that the fibres at the bases of 

 these columns turn under and pass up in con- 

 junction with those of the rope forming the 

 middle mass, cue, at the upper of which 

 they fold over making flat twists upon them- 

 selves, which have, however, become exag- 

 gerated in appearance by the unwinding of the 

 heart, as in rolling it up again some of the 

 angles are converted into spires, preserving a 

 considerable degree of parallelism. 



Having shown the origins, and the method 

 adopted in the association, of the fibres form- 

 ing the middle mass in Jig. 278, we proceed by 

 tracing the divisions and prolongations of its 

 fibres, and the plan of building up the two 

 chambers of the heart. First, the forma- 

 tion of the left ventricle. If the right carnea 

 columna, cc, be replaced in contact with i's 

 fellow, and if the rope, RR, be brought 

 round the upper part of this cavity so as to 

 embrace them, and if portion 4 be split from 

 the middle mass, CRC, and be wound, in 

 association with the apicial fibres, CRC, round 

 the lower part of this cavity, that division of 

 the heart, comprising the left ventricle and the 

 middle mass, will bear a near resemblance to 

 that represented in fig. 280 ; in which figure 

 the rope, RR, in embracing the heads of the 

 carneae columnae, cc, brings into view its fan- 

 like fibres, R, sweeping round the upper part 

 of the axis of this ventricle ; in which the 

 fibres of portion 4, in winding round the lower 

 half of the axis, embrace the bodies of the 

 carnea? columnae, cc, and associate with the 

 apicial fibres, CRC, and in which the ex- 

 tended layer, CRC, represents the middle mass 

 minus the portion 4, which is split from it. 

 Thus much pertains exclusively to the descrip- 

 tion of the formation of the left ventricle. 

 That of the right is more complicated, and 

 constitutes 



