Anatomical symmetry in the hind limbs and spinal motoneurons in frogs.

The weight of muscles and bones of the right and left hind limbs has been studied in 60 frogs. In the first ten frogs studied, the number and size of motoneurons of the seventh, eighth and ninth lumbar spinal segments (which give origin to the sciatic nerve) were studied on both sides. This was done to ascertain the relationship between motoneuron size and limb dominance. No statistically significant difference was observed in the weights of the right and left hind limbs indicating that frogs do not show one-sided hind limb dominance. This result stands in marked contrast to a previous report of asymmetry in bone weight in frogs. Similarly no significant difference was observed in the numerical distribution of neurons and their size between the two sides of the spinal cord.