532 PHILOSOPHICAL TRANSACTIONS. [aNNO 1795. 



cal advantages arising out of them, have been already explained in former lectures 

 on tliis subject ; but there is a form of muscle, in which the disposition of fibres 

 produces a considerable saving of muscular contraction, that has not been at all 

 taken notice of. The muscle I allude to is the heart, the most important in the 

 body, whether we consider the frequency of action, or the office in which that 

 action is employed ; and we shall find on examination, that the fibres are dis- 

 posed differently from those of any other muscle ; which disposition of fibres ap- 

 pears to have a superiority, in being enabled to produce their effect by a smaller 

 quantity of contraction. In considering the muscular structure of the heart, it is 

 only intended to examine that part of it called the ventricles, which may be 

 reckoned '2 separate muscles. The right ventricle, for sending the blood through 

 the vessels of the lungs, called the lesser circulation ; the left, to propel it 

 through the branches of the aorta, which go to every part of the body, called 

 the greater circulation. 



If these 2 ventricles are superficially examined, the muscular partition by which 

 they are united seems to belong equally to both, one half of it appearing to be a 

 portion of the right, the other of the left ventricle. In this view, the sides of 

 the left ventricle, though evidently more muscular and thicker than those of the 

 right, are by no means stronger in proportion to the difference of effects they 

 have to produce. We find however, on dissection, that the septum is almost 

 wholly a portion of the left ventricle, which gives it a great superiority over the 

 other, and makes it capable of performing the important office of supplying the 

 body with blood. 



The left ventricle of the heart, detached from the other parts, is an oviform 

 hollow muscle, but more pointed at its apex than the small end of a common 

 egg. It is made up of 2 distinct sets of fibres, laid one over the otlier in the 

 form of strata ; those which compose the outer set have their origin round the 

 root of the aorta, and in a spiral manner surrounding the ventricle to its apex, or 

 point, where they terminate, after having made a close half turn. The fibres of 

 the inner set, or stratum, are simila » to those of the outer, in their origin, in the 

 mode of surrounding the cavity, a ad in their termination, but their direction is 

 exactly the reverse ; they decussate the outer set in their whole course, and where 

 the 2 sets terminate, they are both blended into one mass. There is an advan- 

 tage gained by this disposition of fibres over every other in the body, which adapts 

 the ventricle so perfectly to its office, that it would almost appear impossible to 

 construct it in any other way, so as to answer the purposes for which it is in- 

 tended. In this muscle, the fibres, by their spiral direction, arc nearly ^ part 

 longer than the distance between the origin and insertion ; and the action of the 

 2 sets being in different directions, renders only -i- the quantity of contraction in 

 each fibre necessary, that would have been otherwise required ; while the turn 



