What reflex is indicated by the extension and splaying of toes when stimulating the lateral plantar surface?

The reflex indicated by the extension and splaying of toes when stimulating the lateral plantar surface is known as Babinski's reflex. This reflex occurs when the sole of the foot is firmly stroked, typically from the heel to the toes, and it is characterized by the big toe extending upward while the other toes may fan out.

Babinski's reflex is an important neurological sign that can indicate the functionality of the corticospinal tract. In adults, the presence of this reflex is often associated with a dysfunction in the central nervous system, as it is typical for adults to exhibit a flexor response (curling of the toes) instead. However, in infants, this reflex is normal and expected due to their immature nervous systems.

The other choices represent different reflexes but do not pertain to the specific response described in the question. Chaddock's reflex involves a similar pathway but uses a different stimulus location on the foot. Oppenheim's reflex is elicited by stroking the tibia and leads to a similar toe response, while clonus reflex refers to a repetitive rhythmic contraction of a muscle and does not involve toe splaying or extension. Thus, Babinski's reflex most accurately fits the description provided.