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XVIII.—The Conducting System of the Marsupial Heart

Published online by Cambridge University Press:  08 April 2017

D. M. Blair
Affiliation:
Universities of Glasgow and Sheffield.
Francis Davies
Affiliation:
Universities of Glasgow and Sheffield.
E. T. B. Francis
Affiliation:
Universities of Glasgow and Sheffield.

Extract

Elsewhere two of the present authors (Davies and Francis, 1941) have expressed theopinion that a specialised cardiac conducting system, consisting of nodal and Purkinje fibres, is a newly evolved one in birds and mammals. The general morphology and topography of this system in the heart of the bird (Davies, 1930 a, 1930 b) is similar to that in the heart of the eutherian mammal, and we have postulated (Davies and Francis, 1941) that the system has undergone parallel evolution in these two classes of homoiothermal vertebrates in response to functional requirements, and that in particular its presence can be correlated with the rapidity of the heart-rate in proportion to its size. On the other hand, Keith and Flack (1907), Keith and Mackenzie (1910), and Mackenzie (1913) maintain that the sinu-atrial node, atrio-ventricular node, and atrio-ventricular bundle of the mammalian heart are remnants of more extensive tissues of similar structure in the hearts of lower vertebrates. They trace the evolution of the conducting system of the mammalian heart from a simpler and more definite form which they described in the fish, and state that as one ascends the animal scale the concentration and reduction of nodal tissue becomes more marked.

Type
Research Article
Copyright
Copyright © Royal Society of Edinburgh 1942

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References

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