about 20 feet by Brunellesco, may be considered as the prototype of
this group; and, indeed it probably suggested it. The fact that we
see in MS. B. 11b (Pl. XCIV, No. 3) by the side of Brunellesco's
plan for the Basilica of Sto. Spirito at Florence, a plan almost
identical with that of the_ Capella degli Angeli, _confirms this
supposition. Only two small differences, or we may say improvements,
have been introduced by Leonardo. Firstly the back of the chapels
contains a third niche, and each angle of the Octagon a folded
pilaster like those in Bramante's_ Sagrestia di S. M. presso San
Satiro _at Milan, instead of an interval between the two pilasters
as seen in the Battistero at Florence and in the Sacristy of Sto.
Spirito in the same town and also in the above named chapel by
Brunellesco.

The first set of sketches which come under consideration have at
first sight the appearance of mere geometrical studies. They seem to
have been suggested by the plan given on page 44 Fig. 2 (MS. B, 55a)
in the centre of which is written_ "Santa Maria in perticha da
Pavia", _at the place marked A on the reproduction.

a) (MS. B, 34b, page 44 Fig. 3). In the middle of each side a column
is added, and in the axes of the intercolumnar spaces a second row
of columns forms an aisle round the octagon. These are placed at the
intersection of a system of semicircles, of which the sixteen
columns on the sides of the octagon are the centres.

b) The preceding diagram is completed and becomes more monumental in
style in the sketch next to it (MS. B, 35a, see p. 45 Fig. 1). An
outer aisle is added by circles, having for radius the distance
between the columns in the middle sides of the octagon.