Comparative development of the bulbus and ventricles of the vertebrate heart with special reference to Spitzer's theory of heart malformations

Abstract

The perennial interest in heart anomalies has produced a variety of discordant explanations for them. Transposition of the great vessels poses an especially difficult problem. One explanation for it, widely accepted by pathologists, is that of Spitzer. Of Spitzer's several papers, the one published in 1923 deals most comprehensively with his theory. This paper has been honored with an extensive paraphrase by Harris and Farber ('39), and recently has been translated and republished by Lev and Vass ('51). Abbott ('36) adopts Spitzer's teaching in her well known Atlas.Spitzer assumes that the hearts of all vertebrates above amphibia evolved from a primitive amniote heart furnished with a small pulmonary artery and two aortae. These higher vertebrates, Spitzer states, led a more and more active life and needed an increasingly efficient respiration. To make this possible, the primitive amniote vessels were modified. In reptiles the pulmonary artery and the left ventricular aorta were enlarged and the right ventricular aorta reduced; in the still more active birds and mammals the right ventricular aorta was done away with altogether. In addition, the interventricular foramen of birds and mammals was closed, thus completely dividing the pulmonary from the general circulation. The evolution of the pulmonary circulation was impelled and directed by teleological and phylogenetic forces, which dominate the ontogeny of the bird and mammal embryo. The abnormal transposition of the aorta of man, in Spitzer's view, is an atavistic revival of the suppressed right ventricular aorta of reptiles.Embryologists have either ignored or opposed Spitzer's theory. For one thing, they have grown wary of mixtures of teleology, phylogeny, and ontogeny. Furthermore, embryologists no longer consider the normal development of an embryo to be a simple recapitulation of ancestral adult forms. De Beer ('58) has amassed evidence for other factors at work within the embryo. The embryos of all higher vertebrates do start with a common structure. But after this common beginning each kind of embryo goes its own way; it may invert the succession of later structures, may introduce novel deviations, may accelerate the growth of some part, or may retain primitive structures lost in other forms, all without regard for adult ancestors. The embryo is much more than a passive register of adult ancestral forms; it has its own spontaneous mutations that produce novel adult structures. All such strictly embryonic factors of development are ignored by Spitzer and his followers.The comparative development of the hearts of the Crocodilia, mammals, and birds offers a good field for the older and newer schools of embryological thought to contend in. The embryos of these three groups start with very similar hearts and arterial arches. All three groups -and they alone -achieve adult hearts with completely divided ventricles and completely separated pulmonary and systemic circulations. Nevertheless, the adult hearts of all three differ considerably, and pass through diff...

Septation and valvar formation in the outflow tract of the embryonic chick heart

“…Such a structure is lacking in the avian heart. Indeed, as pointed out by Shaner (1962), in many respects the avian heart is more comparable in its development to that of sauropsids, including the alligator. These differences are seen both in embryonic and adult features.…”

“…In the chick, there is disagreement about the number of these cushions. Some workers have described only two cushions (de la Cruz et al, 1977;Pexeider, 1978;Icardo, 1990), whereas others have described three (Tonge, 1869;Langer, 1895;Greil, 1903;Hochstetter, 1906;Shaner, 1962;Laane, 1978;Waldo et al, 1998). Of those who recognise three cushions distally, some state that two of them fuse cranially to form a common cushion, but remain unfused caudally (Laane, 1978;Waldo et al, 1998).…”

Evidence for Endothermic Ancestors of Crocodiles at the Stem of Archosaur Evolution

“…The embryology of vertebrate hearts is well known, including specific studies of crocodilians by Greil (1903), Hochstetter (1906), Reese (1915), Wettstein (1954), Goodrich (1958), Shaner (1962), and Ferguson (1985). The authorities agree that the early and intermediate developmental stages are the same in crocodilians and other vertebrates.…”

“…The details of membranous septum development differ between crocodilians, birds, and mammals, but the pattern of circulation is critically dependent on where it joins the three outflow vessels (Shaner 1962). It joins between the left and right arches in crocodiles.…”

Double Outlet Right Ventricle Versus Aortic Dextroposition: Morphologically Distinct Defects

“…In early development, the outflow tract originates entirely from the right ventricle (Shaner, 1962;Van Mierop et al, 1963a;Goor et al, 1972;Anderson et al, 1974;de la Cruz et al, 1981;Lomonico et al, 1986). Counterclockwise conotruncal rotation (looking from the ventricular apex) and the leftward shift of the conoventricular flange normally allow the transfer of the rightsided aortic conotruncus backwards and leftwards above the left ventricle (Goor et al, 1972;Anderson et al, 1974;Lomonico et al, 1986).…”