These seven drawings show a design for the interior elevation of the hall that works through several aspects and details, around the same form. The structure shows a central rectangular doorway framed by two arched niches (in drawings 183 and 184 containing urns).

Above the doorway, drawings 183-185 show a large roundel showing a relief of a chariot, horses and figures. This appears to be a rough sketch of the 'Sol' roundel, cast by Soane's friend Thomas Banks, from the roundel on the side of the Arch of Constantine, Rome. This roundel was eventually to be accompanied by its twin 'lunar' opposite within the vestibule. The triumphal arch theme of the facade (as described in the note for drawing 105, Section 4) is thus continued into the vestibule as is the connection with Soane as the architect to the Bank of England (the same casts had been used on the Lothbury Court).

The section shown in drawing 186 shows the upper part of the vestibule with a rectangular opening, below a ribbed canopy dome and, in the segment supporting the dome, an acroterion enclosing a roundel bearing an indeterminate relief. This upper section clearly dovetails in with drawings 183 and 184.

Drawing 184 also shows various rough sketches in Soane's hand for decorative mouldings and one for a doorway framed by pillars and surmounted by a lunette bearing an urn and two bestial statues. The mouldings shown in drawings 187-189 evidently correspond to the elevation designs.

Helen Dorey suggests that 'The vestibule is a variation on the themes of the facade: while the exterior reflects the structure of the Arch of Constantine, the vestibule reproduces its decoration with the two Banks roundels being interpretations of its antique reliefs of sol and lunar' (op. cit. p.22).

Drawing 183 and 186 show what appears to be an opening in the domed part of the double height vestibule. Drawing 186 shows this continuing into an object above with a strigilated pattern very like the repeated s-shapes of the wrought iron balcony at Lincoln's Inn Fields - it follows that this 'object' may in fact be a circular iron railing protecting the floor opening, which would presumably have drawn light into the vestibule from the roof lantern. Drawing 100 also shows an unlabelled circle positioned above the vestibule, the same opening. However, Soane eventually bought a rosette moulding for the domed ceiling and the opening is unlikely to have every been constructed.