EXPLANATION OF FIGURES

80. Section no. 29, through the caudal border of the chiasma ridge. The dorsomedian ridge and the pars dorsalis thalami cannot be clearly separated at this level.

81. Section no. 41, through the middle of the habenulae.

82. View of the inner surface of the brain of a human embryo of 6.9 mm. Drawn from the wax model by Ziegler of the embryo Br 3 of the His series and lettered after His, '04, p. 56, fig. 34. The region marked C.s. includes not only the corpus striatum but also the preoptic nucleus and other parts of the 1hinencephalon. (1) Maigo reuniens (rhinencephalon with rhinencephalon and pallium).

(2) Margothalamicus (pallium with thalamus, site of the di-telencephalic fissure). (3) Margo peduncularis (corpus striatum with thalamus, site of the sulcus diencephalicus medius).

(4) Margo hypothalamicus (corpus striatum with hypothalamus).

83. Diagrammatic cross section through the diencephalon of Urodela and Anura. On account of the diencephalic flexure, the section must be taken obliquely to the long axis of the brain in the plane A-B of fig. 22, in order to pass transverse to the thalamic axis. The numbers 1, 2, 3 and 4 and the letters A, B and C mark corresponding structures in figs. 83 and 84, the two figures being designed to illustrate the way in which the cerebral hemispheres have been formed by the lateral evagination of the walls of the neural tube; see the text. p. 477.

A, sulcus diencephalicus dorsalis.

B, sulcus diencephalicus medius.

C, sulcus diencephalicus ventralis.

D, roof plate.

V, floor plate.

84. Diagrammatic cross section through the cerebral hemispheres in front of the lamina terminalis of the frog.

A, dorsal angle of hemisphere.

B, zona limitans lateralis and fissuta endo-rhinalis.

C, ventral angle of hemisphere.

D-V, zona limitans medialis and fissure limitans hippocampi.

L.F.T., lateral forebrain tract.

M.F.T., Medial forebrain tract.