Two components of the boundary of \(\text \textbf{I}_3\). (Deux composantes du bord de \(\text \textbf{I}_3\)) Components of Springer fibers associated to closed orbits for the symmetric pairs \((\mathrm{Sp}(2n), \mathrm{Sp}(2p)\times\mathrm{Sp}(2q))\) and \((\mathrm{SO}(2n), \mathrm{GL}(n))\). I. 