Index for the terminology used.

The numbers refer to the superscripts in the Table.
1. Combinations of aortic sac, truncus, conus and bulbus have been used to describe this segment. Conus and bulbus are usually myocardial, whereas aortic sac and truncus refer mostly to the vascular part. Septation from the vascular, semilunar valve and intracardiac levels is interchangeably referred to as either aorto-pulmonary septum or outflow tract (OFT) septum. The endocardial cushions in the proximal intracardiac part myocardialize through induction by neural crest cells forming the aorto-pulmonary or OFT septum. The distal part of the cushions is remodelled into semilunar valves that are separated by fibrous tissue between the orifices of the great arteries. In reptiles the aorto-pulmonary septum is branched and separates the two aortae and the pulmonary trunk. In mammals the distinction between proximal and distal endocardial cushions is inconspicuous.
2.Bulboventricular fold, synonymous with the primary fold, between outflow and inlet portion of the primitive ventricle.
3.Anterior (positional), primary (time-related) and folding (mechanistic, new in this paper) septum are synonymously used. The bulboventricular fold extends apically over the anterior surface of the heart and deepens to enclose epicardium and subepicardial tissue, thus forming an anteriorly located folding septum. The folding septum is considered to be homologous to the reptilian horizontal septum, which is also called the muscular ridge (see for further synonyms ref 13).
4.The apical trabecular septum develops from the coalescence of many trabeculations and does not show a clear demarcation with the folding septum or the inlet septum.
5.The inlet septum in early stages of eventually completely septated hearts and in some reptiles (presence is species-dependent) is a dense muscular structure on the posterior wall of the ventricle without an infolding mechanism. In the current study we have clearly shown that the anterior margin of the inlet septum with the folding septum is formed by the septal band or trabecula septomarginalis. In earlier literature the septal band has been described as the posterior margin of the primary (or folding) septum.
6.The superior and inferior atrioventricular endocardial cushions fuse in the midline. In the central part the cushions are remodelled into fibrous (membranous) tissue that becomes part of the fibrous heart skeleton. Part of this forms the membranous septum which is located between right atrium and outflow of the left ventricle (atrio-ventricular component) and the remainder between RV and LV (interventricular component).This tissue is obliquely embedded in both the atrial and ventricular septa and as such is sometimes referred to as atrioventricular septum.
Index for the terminology used.