Page:Popular Science Monthly Volume 1.djvu/365
NERVOUS CONTROL OF ANIMAL MOVEMENTS.
side experiences a permanent contraction. This attitude is so regular in these lesions that, from simple sight, we can indicate the direction of the movement of rotation. The opposite side has also a constant and typical attitude; the throwing out of the fore-leg from the thorax is always as is shown Fig. 4.
When this frog is placed in water it turns on itself, the right side serving as the axis of movement. When it is at rest in the water, it takes the attitude represented in the figure. The right half of the body sinks in the water; the limbs of this side can never be on a level with those of the opposite side. These last, on the contrary, especially when the cerebral lobes are removed from the two sides, float on the surface and counterbalance the influence of the opposite side; the hind-foot of the uninjured side remains extended, and rests always at a higher level than that of the opposite side; the fore-foot comes out of the water, as well as the anterior part of the body. The limbs of the affected side are not really paralyzed, but, nevertheless, their movements are more limited, they are not so extended nor so various, and their action no longer coincides with that of the healthy side.
If, in place of pricking or deeply wounding one side of the pons Varolii, we prick or wound these nervous centres on each side, a little above the bulb, we obtain a tonic contraction of both sides of the body, and the frog takes the attitude represented in Fig. 5, an attitude due, without doubt, to a tonic contraction of all the muscles of the body. Put in the water, this frog falls to the bottom and remains motionless.
Considering successively the attitudes taken by the frogs from Fig. 2 to Fig. 5, we see perfectly that, when we get beyond the cerebral lobes, all lesion of the other parts of the encephalon leads to a sort of