DETERMINATION OF NEURAL CONNECTIONS
197
stage 23. If the trunk segments were taken from embryos of stage 24,
no movement appeared in the shoulder, but the elbow and wrist still
moved in a coordinated manner. Trunk segments taken from embryos of
stage 25 to 26 could move only the wrist, and the limb remained motionless when it was innervated by older trunk segments. It is difficult to
decide what kind of an axis, if any, might exist along which the trunk
cord lost its capacity to replace the brachial cord. With respect to the
limb, this has happened in a proximodistal sequence.
With the advantageous technique of having the grafted brachial
segments in the same spinal cord with the normal ones, the locomotion
of the supernumerary limbs could easily be compared with that of the
normal fore- or hindlimbs. Lumbosacral spinal cord grafts were also
employed in this experiment, as well as exchanging the brachial cord for
the lumbosacral cord, and the reverse. Extra limbs innervated by the
grafted brachial cord moved in synchrony with the normal forelimbs,
irrespective of whether they were fore- or hindlimbs. Only a slight delay
was detected on slow-motion movie pictures. When lumbosacral segments were grafted into the trunk region, the extra limbs moved in
synchrony with the hindlimbs, although a greater or smaller delay was
found in most of the cases. After exchanging the brachial segments for
the lumbosacral segments, or the reverse, there was no strict correlation
in the movement of the four limbs. A strong tendency of the limbs on the
same side to move in parallel was, however, recorded. By similar embryonic transplantations of spinal cord segments in chickens, Straznicky
(1963) succeded in showing that, after exchanging the brachial for lumbosacral segments, the wings moved completely in parallel with the legs
on the same side after hatching.
There was another interesting feature of the function of limbs innervated by heterotopic cord segments. When a forelimb was moved by
lumbosacral segments, the elbow remained relatively motionless, just
like the knee in a normal hindlimb. This was more apparent in the chick.
A wing with lumbosacral innervation was unable to perform winglike
fluttering movements; there was only an elevation and abduction of
moderate excursion in the shoulder and a very little extension in the
elbow, in parallel with leg movements. Similarly, if a leg was grafted
into the place of a wing in otherwise normal embryos, the leg showed a
typical winglike movement in the hip with little or no movement in the
knee and in the ankle, although the musculature of the grafted leg and
the peripheral innervation was complete (Straznicky, 1963). The character of the movements was thus determined by the nature of the innervating segments.
The other aspect of coordinated limb function is the proper connec-
197
stage 23. If the trunk segments were taken from embryos of stage 24,
no movement appeared in the shoulder, but the elbow and wrist still
moved in a coordinated manner. Trunk segments taken from embryos of
stage 25 to 26 could move only the wrist, and the limb remained motionless when it was innervated by older trunk segments. It is difficult to
decide what kind of an axis, if any, might exist along which the trunk
cord lost its capacity to replace the brachial cord. With respect to the
limb, this has happened in a proximodistal sequence.
With the advantageous technique of having the grafted brachial
segments in the same spinal cord with the normal ones, the locomotion
of the supernumerary limbs could easily be compared with that of the
normal fore- or hindlimbs. Lumbosacral spinal cord grafts were also
employed in this experiment, as well as exchanging the brachial cord for
the lumbosacral cord, and the reverse. Extra limbs innervated by the
grafted brachial cord moved in synchrony with the normal forelimbs,
irrespective of whether they were fore- or hindlimbs. Only a slight delay
was detected on slow-motion movie pictures. When lumbosacral segments were grafted into the trunk region, the extra limbs moved in
synchrony with the hindlimbs, although a greater or smaller delay was
found in most of the cases. After exchanging the brachial segments for
the lumbosacral segments, or the reverse, there was no strict correlation
in the movement of the four limbs. A strong tendency of the limbs on the
same side to move in parallel was, however, recorded. By similar embryonic transplantations of spinal cord segments in chickens, Straznicky
(1963) succeded in showing that, after exchanging the brachial for lumbosacral segments, the wings moved completely in parallel with the legs
on the same side after hatching.
There was another interesting feature of the function of limbs innervated by heterotopic cord segments. When a forelimb was moved by
lumbosacral segments, the elbow remained relatively motionless, just
like the knee in a normal hindlimb. This was more apparent in the chick.
A wing with lumbosacral innervation was unable to perform winglike
fluttering movements; there was only an elevation and abduction of
moderate excursion in the shoulder and a very little extension in the
elbow, in parallel with leg movements. Similarly, if a leg was grafted
into the place of a wing in otherwise normal embryos, the leg showed a
typical winglike movement in the hip with little or no movement in the
knee and in the ankle, although the musculature of the grafted leg and
the peripheral innervation was complete (Straznicky, 1963). The character of the movements was thus determined by the nature of the innervating segments.
The other aspect of coordinated limb function is the proper connec-