Licence: Public Domain Mark
Credit: Heart / by John Reid. Source: Wellcome Collection.
Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.
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![HEART. vyhich are apparently of the same number and thickness ass in that portion of the artery im- mediately above, form a distinct curved edge (fig. 2, ej, as they pass from the extremity of one festoon to the other. As we trace tiie middle coat of the artery downwards into the concavities formed by each festoon, we find that below this curved edge they become stri- kingly thinner and continue to diminish in thickness and in length, (since they can only stretch between the projecting extremities,) until we arrive at the bottom of the concavity. These three thin portions of the middle coat must then be placed behind the semilunar valves, and correspond to the sinuses of Val- salva.* The thinness of the middle coat at the sinuses of Valsalva will render this portion of the artery more dilatable, and predispose it to rupture when its coats are diseased.f The tendinous zones are distensible, but to a con- sklerably less extent than the middle coat of the arteries. I am not aware that this account of the manner in which the middle coat of the arteries is attached to the tendinous rings has been previously given. I suspect, however, that Dr. Duncan must have been perfectly aware of it from some parts of his manuscript. The differences between these tendinous fes- toons and the yellow elastic coat of the arteries, and the manner of their attachment, can easily be made out in the human heart; they are, however, more apparent in the larger animals' as the horse and ox. The different characters' of the two tissues are obvious at the first glance after boiling, even in the human heart. Muscular tissue.%—The. greater part of the * So striking is the difference between the middle coat as it fills up the concavity of these festoons, and where it stretches between the projecting ex- tremities in the hedgehog, that at first sight ft ap- pears to be deficient at that part. + According to Valsalva aneurisms are frequently found in this situation : Atque hie aoitse sinus maxiinus ille est, in quo saepe aneurysmata circa prscordia contingunt, ut propria obscivalione edoctus sum. Valsalvae Oppra. Epist. Anat. ed. Morgagni, torn. i. p. 131 1740. This greater tendency to aneurismatic dilatation must depend upon two circumstances. The increased calibre of the artery at this part will increase the pressure upon its walls from the well-known hydrostatic law, that in a quantity of fluid submitted to compres- sion, the whole mass is equally affected, and simi- larly in all directions, and the diminished thick- ness of the middle coat will materially favour this distending force. X While I was engaged in examining the arrange- ment of the muscular fibres of the heart. Dr. Alison had the kindness to procure for me the manuscript of the late Dr A.Duncan, jun. on this subject. It was well known not only in this country but on the continent that Dr. Duncan had for a very long pe- riod attended very particularly to this question, and was in the habit of demonstrating the parts he had ascertained to his pupils. Unfortunately his inten- tions of publishing on the subject were never car- ried into execution, and his papers referring to it were left in so confused a state that it is exceed- ingly difficult and in most parts impossible to make out the description. I have availed myself of those parts that are legible in the following pages, and these I have scrupulously acknowledged. Dr. Dun- can's dissections of the heart were taken entirely from the ox and sheep. heart is composed of muscular fibres arranged m a very intricate manner. These fibres are connected togellier by cellular tissue,* which, however, exists in much smaller quantity in the heart than in the other muscles of the body Ihese fibres are attached generally by boil extremities to the tendinous rings situated around the orifices of the heart; the fibres of the auricles pass upwards to form the auricles, and those of the ventricles downwards to form' the ventricles, so that these tendinous rings must form the fixed points towards which all the contractions.of the heart take place. None of the muscular fibres of the auricles are con- tinuous at any part with those of the ventricles, and we will find that while some of them are confined to a single auricle, others belong to both. In the same manner a great part of the fibres of the ventricles are common to both, and are interwoven together, while others again belong exclusively to a single ventricle, or, as Winslowf expressed it, the heart is com- posed of two muscles enveloped in a third. The intimate arrangement of these muscular fibres, particularly those of the ventricles, is exceedingly complex, as the contraction of the organ is not in one particular direction only, but in all directions, atid has long been con- sidered as a kind of Gordian knot in anatomy. Vesalius, Albinus, and HallerJ confessed their inability tp trace them, and more lately De Blainvil]e§ assures us, from his own experi- ence, that we can only arrive at very general conclusions (des choses ins-gtnirales) on this subject. By adopting the method of long- continued boiling of the organ before com- mencing to attempt to trace the course and ar- rangement of its fibres, we will find that after a few trials several of the most important points connected with the distribution of these can be ascertained, and by perseverance they can be unravelled to a great extent. By long boiling the muscular fibres are rendered hard and firm while the tendinous and cellular tissues are softened or dissolved, and the fat melted. Dr. Duncan, who employed this method to a great extent, stales that the essential circumstance is to continue the boiling long enough, and that he has never been able to carry it too far. I have found from eighteen to twenty hours gene- rally sufficient for this purpose. Some have recommended that the heart should be pre- viously put for a slioi t time into a strong solu- tion of salt, and Vaust advises that it should be boiled in a solution of nitre, for the purpose of rendering the fibres firmer. The boiling is infinitely superior to the maceration in vinegar. By stopping the boiling before the tendinous rings are rendered too soft, we can easily see their form and their connexions to the muscular fibres. The general connexion and distribution of » [This ho wever is denied by other obscrverSt and from very recent and careful examinations. See the succeeding article by Mr. Searle.—Ed.] t Mcmoires de I'Academie Royalc des Sciences, 1711, p. 197. t El. Phys. torn. i. p. 351. d Cours de Physiologic, S:c. torn. ii. p. 359.](https://iiif.wellcomecollection.org/image/b21908503_0018.jp2/full/800%2C/0/default.jpg)
