The basial band crosses the upper half of this ventricle. It cannot be raised from its situation on account of the numerous lateral connexions it forms in its progress with the margins of the orifices of the aorta, pulmonary artery, and annulus venosus. In order to de tach it as far as it will admit, an incision about half an inch on the right side of and parallel with the anterior coronary track, should be made, extending from its lower edge to the base, and an eighth of an inch in depth, or as deep as will expose the fibres from the pulmo nary artery, which in general pass at an angle with those of the band. Although this band cannot be disconnected from the base, it can in general be detached from the fibres of the sub jacent layer, so far as the posterior coronary track ; sometimes, however, they are too inter woven to admit of any separation. The first part of this band is represented in fig. 281, marked CPCAA it was divided more than half an inch from the anterior coronary track. Its continuation may be seen in fig. 282, lettered CPCAAA, where it is evidently not discon nected from, but merely raised towards the base, and if replaced would overlap the fibres taking the middle course round the heart. The depression at the line of the posterior coro nary track, pet, is occasioned by the band being bound down at the base and at its under sur face also, by which means the upper half of the posterior boundary of this ventricle is formed. As the further pursuit of this band pertains to the third stage, it will be made hereafter.
The internal layer. By the separation of the two former bands the internal layer is ex posed. It is composed of fibres from the pul monary artery and from one of the carnew co lumnm. In fig. 281 the fibres, cc, are seen arising from the root of the pulmonary artery at its entire circumference, first forming a channel and then expanding into a layer, which, in pro ceeding obliquely across the cavity, obtains an accession of fibres from one of the carnew co lumnar, which is not brought into view, and which, on reaching the line of the posterior coronary track, joins a band emerging from the septum, and thus forms the apicial half of the posterior boundary of this ventricle. It is raised from its situation, but when replaced its edge, which is everted by the probe, applies itself to the anterior boundary of this cavity. This layer cannot often be so extensively dis connected from its superjacent bands as this figure represents.
The third stage of the dissection.-11aving separated the layers composing the right or proper wall of the right ventricle, the next pro ceeding consists in detaching and unwinding the band and layers composing the left ventri cle. First, the detachment of the basial band. As this band has already been detached over the right ventricle in the second stage of the dissection, it is necessary to resume its separa tion at the posterior coronary track. But as the further separation is somewhat difficult, it will be rendered less so if the remaining portion of this band be first examined in fig. 282,
wherein it is represented detached. When in its natural situation it forms the uppermost third of this, the left ventricle, and its lower fibres overlap a part of those which occupy the middle third. The fibres which overlap the others in taking an oblique course towards the base reach the brim of the ventricle and pass over it, while the under fibres of this band are appearing in succession, and taking a similar spiral course until the whole bundle of fibres is twisted in the form of a rope. In order, there fore,to trace ou t and detach this band as it becomes transformed into a rope, it is requisite to com mence near the posterior coronary track (pet), in a continuous line with the lower edge of its former portion, introducing the handle of a scalpel obliquely upwards so as to detach the fibres which overlap those of the middle third, and to carry the separation so far up as will reach those marked A, coming obliquely down from the aorta. In conducting this separation from left to right it is soon found that the fibres of this bundle, instead of overlapping others, become themselves by twisting overlapped, rendering it necessary, therefore, to turn gra dually the handle of the scalpel obliquely downwards, tracing the rope according to its windings. Two scalpels will be required in conducting the further separation.
The next step should be preceded by viewing the fibres of the rope in Jig. 280, descending and radiating into a layer which sweeps round the cavity of this ventricle. The heart should COW be placed in a small cup or jar of a size that will support it with its base upwards, and then, with the scalpels employed vertically, the separation should be proceeded with, and in passing through the septum a vertical section should be made through the aorta in the line of separation, which should be pursued round and round, and progressively deeper until the handles of the scalpels perforate the external fibres, which, if they have been rightly inclined, they will do a little above the apex of the left ventricle, just after they have completed the division through the layers of the septum. The band of fibres occupying the middle third of the heart, and which now pass over the scal pels, should be divided ; the incision being made along the side of the posterior edge of the septum. A section should be made through the rope also, which allows the right ventricle to be raised from the left, and the heart to be unwound as far as the separation has been car ried. There yet remains a mass of fibres around the cavity of the left ventricle to be de tached. This last process of separation should be conducted in a contrary direction to that which has hitherto been adopted, viz. from right to left, until the internal membranous lining is exposed, and which should be torn in order to lay open this chamber.