Freiburger historische Bestände - digital

274

Cunningham Memoirs.

stem is always developed in one piece, but the horizontal limb may arise
from the union of a posterior and an anterior depression. We have already
noted that in 8'5 per cent, of the adult hemispheres examined, a deep
annectant gyrus intervened between the horizontal and vertical parts of the
inferior prsecentral sulcus, and, further, that in 2*1 per cent, this gyrus was
observed on the surface ; a deep annectant gyrus was also in rare instances
seen at the base of either the anterior or posterior portions of the horizontal
ramus. All these conditions are explained by the manner in which the
sulcus is developed.

Fig. 62.—Lateral view of the right hemisphere of a fcetus in the latter part of the seventh month of

development. Drawn by the American apparatus for tracing orthogonal projections of
the skull.

r. . . Fissure of Rolando. p. e. i. . Sulcus preecentralis inferior.

p. c. s. . Sulcus pracentralis superior. i. t. . . Sulcus transversus of the fissure of Rolando.

f.1 . . Sulcus frontalis superior. f.2 . . Sulcus frontalis inferior.

p. c. m. . Sulcus prsecentralis medius. /. m. . Sulcus frontalis medius.

In figure 60, p. 268, a foetal brain well on in the seventh month of
development is represented, in which the horizontal portion of the furrow
is still separate from the vertical stem.

We have already mentioned that in the last two or three months of
foetal life, the horizontal limb of the sulcus prsecentralis inferior is, as a
rule, more evident, and apparently more distinctly sagittal in its direction
than in more advanced stages of growth. Figure 61 is a good example
of this {vide also fig. 54, p. 250; fig. 55, p. 251 ; PI. i., fig. 33).

The condition exhibited in the above figure (fig. 62) is interesting.