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XII. — The Development of the Heart in Man. By Prof. D. Waterston, M.D., 
Bute Medical School, University of St Andrews. (With Eighteen Text- 
figures and Sixteen Plate-figures.) 
(Read July 9, 1917. MS. received December 26, 1917. Issued separately August 1, 1918.) 
Introduction. 
Examination of living embryos has shown that the heart is a functionally 
active organ from a very early stage of its development. At all periods of life 
the result of the functional activity is in essentials the same, viz. the propulsion 
of the blood in a definite direction through the heart into the vessels arising from 
it; but the mechanism for effecting this propulsion undergoes profound alterations, 
and the heart becomes transformed from a simple continuous tube, destitute of 
valves, whose walls contract in a rhythmic peristaltic wave, into a complex four- 
chambered organ, divided into right and left portions, which are ultimately com- 
pletely separated from one another, possessing valves, and contracting not in a 
peristaltic wave but in alternating consecutive contractions of the atria and 
ventricles of the right and left sides simultaneously. Coincidently with the 
changes in the heart itself, profound alterations occur in the vessels leading to 
and from the heart. In this combination of simultaneous development and 
functional activity the heart differs from the other organs of the body, and hence 
its development presents special problems involving the function as well as the 
structure of the different parts. Our knowledge of the development of the heart 
in man cannot yet be said to be complete. 
The discovery by Kent and His of connections between the atria and ventricles, 
and that by Keith and Flack of the sinu-atrial node, with the consequent altered 
views of the mechanism of the heart-beat which are now generally accepted, have 
imparted a new interest and value to the study of the development of the heart. 
The development of the atrio-ventricular bundle has been worked out by Mall, 
but the records of examination of at all complete series of the hearts of human 
embryos are as yet scanty. The introduction of the plate method of reconstruction 
provided a new method of great value to embryologists, particularly in the study 
of the development of the heart, since without accurate plastic reconstructions it 
is almost impossible to follow the complex three-dimensional changes which occur, 
and hence those descriptions alone are of special value in which this method has 
been employed. 
The embryonic material examined in this investigation includes human embryos 
from 3 mm. to 30 mm. in length (maximum) cut in serial section, and a number of 
larger embryos. 
TRANS. ROY. SOC. EDIN., YOL. LII, PART II (NO. 12). 
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