The heart can now be unwound and extended as in fag. 278, placing the left ventricle, lv, at one end and the right at the other, removing that section of the aorta, AA, connected to the right ventricle from its counterpart which ex clusively pertains to the left, and which is hid den by the rope, art ; removing also the two portions of the bisected rope to the two most distant diagonal points in this view. The niche, CPC, indicates the part occupied by the divided band which passed along the mid dle third of the heart.
The second method of demonstration.—The formation, or winding up of the fibres, of the heart. This description comprehends the retracing of the fibres from the centre to the circumference, showing their respective origins, associations, courses, connexions, and terminations, also the manner in which they are wound up to form the two ventricles into one compact conical body.
7he first stage consists in retracing the su perficial layer from its origins to its termina tions. It is necessary to commence at the very centre of the heart—the interior of the left ventricle, whence spring the fibres composing its main bulk. Fig. 278, at its right extremity, exhibits the left ventricle, lv, laid open, exposing the two carnere columm, cc and cc, one of which is placed out of its situation, in order to show the interior of the chamber. The fibres of the two carnem columns', cc and cc, ex pand in a fan-like manner ; those of the rope, an, expand in a similar manner ; the radiated fibres of each of these three bodies wind round the axis of this ventricle forming its txtrietes ; and as they wind so as to form an inverted cone, it is clear that the inmost fibres alone can reach the apex. Accordingly, a faseiculus of the inmost fibres from each of these three bodies, marked c, and c respectively, pass down to the apex associated together, and in their course make a gentle twist from left to right, gradually contracting the cavity to a point and it; they then twist sharply round upon each other and complete the apex marked cue conjointly, so that by means of this twisting the internal fibres are rendered external. These excluded fibres now enter into the formation of the superficial layer, and form the tail of fig. 279. They take a very spiral course near the apicial part, and over the an terior surface of the left ventricle as far as the anterior coronary track ; but as they approach 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, ccc. 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 fig. 281 these accessory fibres from the aorta, AA, and from two of the carne columnw, 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 fig. 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.