A textbook of human physiology / translated from [the] 6th German edition by W. Stirling.

  • Landois, Leonard
Date:
1888
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Licence: Public Domain Mark

Credit: A textbook of human physiology / translated from [the] 6th German edition by W. Stirling. Source: Wellcome Collection.

Provider: This material has been provided by Royal College of Physicians, London. The original may be consulted at Royal College of Physicians, London.

    103/980 page 51
    STRUCTUEE AND MUSCULAR FIBRES OF THE HEART. capsules, and the frog in its kidnej^s. When an artery splits up into fine branches during its course, and these branches do not form capillaries, but reunite into an arterial trunk, a rete mirabile is formed, such as occurs in apes and the edentata. Microscopic retia mirabilia exist in the human mesentery (Schobl). Similar arrangements may exist in couuectiou with veins, giving rise to venous retia mirabilia. ^ 43. THE HEART.—The muscular fibres of the mammalian heart consist of short (50 to 70 ^ in man), very tine, transversely striated fibres, which are actual unicellular elements, devoid of a sarcolemnia (15 to 25 fx broad), and usually divided at their blunt ends, by which means they anastomose and form a network (fig. 26, A, B). The individual muscle-cells contain in their Fig. 26. A, muscular fibres from the heart of a mammal, and C from a frog ; 13, transverse section of the cardiac fibres; b, connective-tissue corpuscles ; c, capillaries. centre an oval nucleus, and are hekl together by a cement which is blackened by silver nitrate, and dissolved by a 33 per cent, solution of caustic potash. This cement is also dissolved by a 40 per cent, solution of nitric acid. The transverse strife are not very distinct, and not unfrequently there is an appearance of longitudinal striation, produced by a number of very small granules arranged in rows within the fibres. The fibres are gathered lengthwise in bundles, or fasciculi, surrounded and separated from each other by delicate processes of the perimysium. When the connective-tissue is dissolved by prolonged boiling, these bundles can be isolated, and constitute the so-called fibres of the heart. The transverse sections of the bundles in the auricles are polygonal or rounded, while in the ventricles they are somewhat flattened. [The muscular mass of tlie heart is called the myocardium, and is invested by fibrous tissue. It is imjjortant to notice that the connective- tissue of the visceral pericardium (epicardium) is continuous with that of the endocardium by means of the perimysium surrounding the bundles of muscular fibres.] The fine spaces which exist between these bundles form narrow lacunie, lined with epithelium, and constituting part of the lymphatic system of the heart. [The cardiac muscular fibres occupy an intermediate position between striped and plain muscular fibres. Although they are striped, they are involuntary, not being directly under the influence of the will, while they contract more slowly than a voluntary muscle of the skeleton.] In the frog's heart the muscular fibres are in shape elongated spiiulles, or fusiform, in this respect resembling the \Aa.m muscle-cells, but they are transversely striped (fig. 2(5, C). They are easily isolated by means of a 33 per cent, solution of potash or dilute; alcohol. 44. ARRANGEMENT OF THE CARDIAC MUSCULAR FIBRES.—The study of the embryonic heart is the key to a proper understanding of the coni[)licated arrangement of the fibres in the adult heart. The simple tubular heart of the embryo has an outer circular and an inner longitudinal layer of fibres. The septum is formed later ; hence, it is clear that a part, at least, of the fibres must be common to the two auricles, and a part also to the two ventricles, since there is, originally, but one chamber in the heart. The muscular fibres of the auricles are, however, completely separated from those of the ventricles by the fibro-cartilaginous rings. In the auricles the fundamental arrangement of the embryonic fibres partly remains, while in the ventricles it becomes obscured as the cavities undergo a sac- like dilatation, and also become twisted in a spiral manner.
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