ON THE ARRANGEMENT OF THE FIBRES OF TILE IIEART.—[The Editor hopes that the following detailed account of the researches of Mr. Searle on this difficult point of minute anatomy will not be deemed unacceptable. Any reference to the labours of other anatomists has been rendered unnecessary in consequence of that part of the preceding article which bears upon this subject.] Preliminary ronarks.—In order to unravel the fibres composing the ventricles of the heart, considerable preparation is necessary. The auricles, fat, coronary vessels, and external pro per membrane should be cleanly dissected off; the heart should then be boiled thoroughly, but not too much, so as to give its fibres the requi site degree of firmness without rendering them fragile. For example : sheep's hearts should be boiled ten or fifteen minutes ; calves' twenty or thirty, and bullocks' forty or fifty minutes ; immediately afterwards they should be im mersed in cold water ; for if they be exposed to the air while hot, their superficial fibres be come dark, dry, and brittle. As the process of unravelling occupies many hours, and as the heart requires to be preserved in a good condi tion, it should be immersed during the intervals in weak spirit and water. The heart of the calf is preferable to that of any other animal, it being on a scale which affords distinct views, while the fibres of young are more easily sepa rated than those of older animals. The con formation is the same in all quadrupeds, and bears a complete resemblance to that of the human heart. When the coronary vessels are dissected off, a depressed line or track is left on the anterior and posterior surfaces of the heart. Since this line corresponds externally to the entire edge of the septum, and to the boundary of the right ventricle, it may be usefully em ployed in reference to these paits. It is there fore denominated the anterior or posterior co ronary track, accordingly as it pertains to the anterior or posterior surface of the heart.
The fibres of the heart are not connected together by cellular tissue as are those of other muscles, but by an interlacement which in some parts is very intricate, and in others scarcely perceptible. At the entire boundary of the right ventricle they decussate, and become greatly intermixed ; at the apex and base of the left ventricle they twist sharply round each other, and so become strongly embraced ; but in ge neral the interlacement is so slight tbat they appear to run in parallel lines. Whether a mere fasciculus or a considerable mass of this last description of fibres be split in the direc tion of the fibres, a number of delicate parallel fibres will present themselves, some being stretched across the bottom of the fissure per fectly clean and free from anyconnecting medium whatever; and although some must necessarily be broken, yet these are so few that they do not attract attention unless sought for. In this process of separation very little resistance is offered ; and none that is appreciable when a single fibril is taken hold of by the forceps, and stripped off, and which could not be done if bound down by cellular membrane.
If a piece of common muscle be afterwards split, it will be found to offer great resistance, and to be attended with so much laceration of the fibres, that instead of a beautiful series of fine muscular threads arranged in parallel lines, a ragged mass of mutilated fibres appears; and during the process of separation, the cel lular substance is seen not only to connect the fibres, but to afford the resistance which is ex perienced.
This comparison obtains in the undressed state of the specimens ; but when cooked, other distinctions are met with. For example : in whatever direction a roasted heart be sliced, its cut surface is uniformly smooth, not grained like other muscles when dressed ; and it eats short, not offering that elastic resistance which other muscles do during mastication.