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PLATE III.

[The Mesial Face of the Cerebral Hemisphere of the Human Foetus at different.stages of development. The various

figures were drawn on the stone from photographs.]

LETTERING COMMON TO ALL THE FIGURES.

f. a. a. . Fissura arcuata anterior.
/. a. p. . Fissura arcuata posterior.
c. m. . Calloso-marginal sulcus.
c. . . Calcarine fissure.

c.1 . . Tho "stem" of the calcarine fissure or the anterior
calcarine fissure.

p. o.
c. I.

. The fore piece of the secondary posterior calcarine
sulcus.

. The hinder piece of the secondary posterior calcarine
sulcus.
. The parieto-occipital fissure.1
. Collateral fissure.

Figures 1 and 2,—The two cerebral hemispheres from a foetus in the twelfth week of development.

Figures 3 and 4.—The two cerebral hemispheres from a foetus in the first half of the fourth month of development:
probabty the fourteenth week.

Figures 5 and 6.—The two cerebral hemispheres from a foetus in the second half of the fourth month of development
(fifteenth or sixteenth week).

Figures 7 and 8.—The two cerebral hemispheres from a foetus in the early part of the fifth month of development.

Figures 9 and 10.—The two cerebral hemispheres from a foetus in the middle of the fifth month of development.

Figure 11.—The right cerebral hemisphere from a foetus in the early part of the fifth month of development.

Figure 12.—Tho left cerebral hemisphere from a foetus in the latter part of the fifth month'of development.

Figure 13.—The right cerebral hemisphere from a foetus in the beginning of the sixth month of development.

Figures 14 and 15.—The two cerebral hemispheres from a foetus approaching the middle of the fifth month of development
.

Figures 16 to 19.—The four cerebral hemispheres of two female foetal twins in the early part of the sixth month of
development. They represent the mesial aspect of the same hemispheres which are figured in Plate II. (Figures 12 to 15.)
Note that in Figure 19 the letter "c.1" should be "o.2"

Figures 20 and 21.—Tho two cerebral hemispheres from a foetus at the end of the fifth month of development.

Figure 22.—The left cerebral hemisphere of a foetus in the early part of the sixth month of development.

Figure 23.—The right cerebral hemisphere of a foetus in the middle of the sixth month of development.

Figure 24.—Right cerebral hemisphere in the first week of the sixth month of development.

Figures 25 and 26.—The two cerebral hemispheres from a foetus in the beginning of the seventh month of development.
Figures 27 and 28.—The two cerebral hemispheres of a foetus in the early part of the seventh month of development.
Figure 29.—Right cerebral hemisphere of a foetus at the end of the sixth month of development.

ROYAL IRISH ACADEMY.—CUNNINGHAM MEMOIRS, NO. Til.

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