[Lack of attachment of the superior vena cava to the mediastinum. Apropos of 2 cases].

Two cases in which the superior venae cavae ran an extramediastinal course are presented. This abnormality, which was discovered on catheterisation, had no haemodynamic consequences. It consisted of two superior venae cavae with little or no intermediate trunk; this explains the lack of attachment' of the superior venae cavae to the mediastinum.