On some of the causes and effects of valvular diseases of the heart : being the Croonian Lectures of the Royal College of Physicians for 1865 / by Thomas B. Peacock.

  • Peacock, Thomas B. (Thomas Bevill), 1812-1882.
Date:
1865
Catalogue details

Licence: Public Domain Mark

Credit: On some of the causes and effects of valvular diseases of the heart : being the Croonian Lectures of the Royal College of Physicians for 1865 / by Thomas B. Peacock. Source: Wellcome Collection.

Provider: This material has been provided by the Francis A. Countway Library of Medicine, through the Medical Heritage Library. The original may be consulted at the Francis A. Countway Library of Medicine, Harvard Medical School.

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    the semilunar valves, at the origin of the aorta and pulmonary artery, may be originally either too many or too few in num- ber. The mode in which the valvular apparatus is developed we do not know, but it seems probable that each segment is originally composed of two portions, more or less completely divided, which subsequently become blended together. Thus when the number of valves is in excess, the condition is, I be- lieve, always due to the occurrence of supernumerary valves, which are only partially separated from some of the other segments, so as apparently to indicate an imperfect blending of the curtains together. If this be correct, the excess in the number of the valves is not the result of redundant develop- ment, but of an arrest of the proper process of growth. We thus frequently meet with four semilunar valves, sometimes with five, and on the view suggested there is no reason why there should not be six, though I have never in any instance seen that number. When the number of the valves is defective there may be only two segments, or the apparatus may consist of a single imperfectly-formed curtain. In cases of this descrip- tion I conceive that the defect is due to a process alto- gether different from that which occasions the former condi- tion. It seems most probable that the segments are origi- nally correctly formed, but, during foetal life, the angles and contiguous sides of two or more of the valves become adherent, and the band of membrane which indicates the line of union subsequently becomes atrophied and more or less completely disappears. Thus, when only two curtains are found they are generally of very unequal size; the upper or arterial surface of the larger fold is marked by a membra- nous ridge, extending from the edge of the valve to the wall b 2