The diaphragm in man : a record of our present knowledge of its development, relationships, structure, and mode of action / by J.F. Halls Dally.

  • Dally, John Frederick Halls, 1877-1944.
Date:
[1908?]
Catalogue details

Licence: In copyright

Credit: The diaphragm in man : a record of our present knowledge of its development, relationships, structure, and mode of action / by J.F. Halls Dally. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    disposition. Thus the fibrous portion is inelastic and incon- tractile, whilst the muscular part contracts with an effect which varies directly with the length and cross-section of its fibres, and the resistance—variable or constant—which is offered to their action. Of the muscular portion the sternal fibres are much the shortest and least active ; the middle fibres of the crura are the longest and play the most active part; while the peripheral band springing from the costal margin is inter- mediate in lengtli and power. This does not meaTi, however, that the diaphragm will be drawn down proportionately to the length and strength of muscle-tissue in particular regions, since, as stated above, the resistance of the contiguous struc- tures in various situations is various. The function of the crura is to pull down the mediastinal structures through the medium of the pericardium, which is inelastic. Hence, although it might be thought that the posterior portion of the central tendon would move most on account of the attachment of the crural fibres to the posterior border, constituting, as they do, by far the longest and strongest portions of the muscle, yet, as a matter of fact, although its downward movement is greater than that of the anterior portion, it does not possess as much movement as the domes. Much of the energy of the crura is absorbed in swinging the liver downwards and forwards. The direction of the fibres, too, must be taken into account, the sternal fibres, which, on moving downward have assumed a more horizontal course, can only act by pulling inwards the lower end of the sternum, and have but little further action in drawing down the central tendon. “ For the effective contrac- tion of this muscle its attachment to the lower ribs is kept fixed by the contraction of the quadratus lumborum ” (®^). A link may be found to connect the active with the passive move- ment of the diaphragm in that this muscle by its own con- traction helps to expand the lower aperture of the thorax. A condition of tonus of the abdominal muscles is necessary in order that this expansion should take place through the push- ing forwards of the belly-wall in the neighbourhood of the attachment of the anterior musculature to sternum and costal cartilages. If one watches the movement of the diaphragm in a live rabbit one cannot fail to be struck with the way in which descent of this muscle is induced by the simultaneous contrac- tion of the powerfully acting crura. This contraction probably causes the slight depression above referred to, which is at times manifest on orthodiagraphic examination a little external to the summit of the curve when the diaphragm is acting