108
ARTHUR
HUGHES
25 h
10
15
20
Days of development (mouse)
FIG. 12. Correlation of data for development of behavior in rat embryo with
that for cell numbers in ventrolateral column of mouse embryo. Scale of days on
each coordinate. The number of cells in the ventrolateral column of the mouse
cord falls from the eleventh to the fifteenth day, with a peak of degeneration at
13 days (Harris, 1965). At the corresponding period in the rat (15 days), reflex behavior has not yet begun (Windle et al., 1935). By 17 days, the segregation of cell
groups in the motor column of the rat is almost complete (Angulo y Gonzalez,
1940). Limb motility in the rat develops mainly during the eighteenth and nineteenth days (Swenson, quoted by East, 1931).
which, however, is not simultaneous at all levels of the cord but progresses
in a craniocaudal wave. Although the genesis of motility in the limbs of
the fetal mouse has not yet been studied, the development of mouse and
rat can be correlated by comparison of the time of birth of each species
and the changes in the external features of each fetus, as given by Harris
and by Witschi (1956). From Fig. 12 it would be expected that the main
period of cell degeneration is largely over before the appearance of
motility in the limbs. In the rat, Angulo y Gonzalez (1940) found that
the segregation of each ventral horn into columns was almost complete
by the seventeenth day, a time when limb movement is most rapidly
developing.
Days of development (rat)
ARTHUR
HUGHES
25 h
10
15
20
Days of development (mouse)
FIG. 12. Correlation of data for development of behavior in rat embryo with
that for cell numbers in ventrolateral column of mouse embryo. Scale of days on
each coordinate. The number of cells in the ventrolateral column of the mouse
cord falls from the eleventh to the fifteenth day, with a peak of degeneration at
13 days (Harris, 1965). At the corresponding period in the rat (15 days), reflex behavior has not yet begun (Windle et al., 1935). By 17 days, the segregation of cell
groups in the motor column of the rat is almost complete (Angulo y Gonzalez,
1940). Limb motility in the rat develops mainly during the eighteenth and nineteenth days (Swenson, quoted by East, 1931).
which, however, is not simultaneous at all levels of the cord but progresses
in a craniocaudal wave. Although the genesis of motility in the limbs of
the fetal mouse has not yet been studied, the development of mouse and
rat can be correlated by comparison of the time of birth of each species
and the changes in the external features of each fetus, as given by Harris
and by Witschi (1956). From Fig. 12 it would be expected that the main
period of cell degeneration is largely over before the appearance of
motility in the limbs. In the rat, Angulo y Gonzalez (1940) found that
the segregation of each ventral horn into columns was almost complete
by the seventeenth day, a time when limb movement is most rapidly
developing.
Days of development (rat)