In the heart muscle during a brief period after each beat, that is, after each single contraction of the rhythmic series, the muscle becomes inexcitable.
It cannot then be excited to contract by any agent, though the inexcitable period is more brief for strong than for weak stimuli.
The motor field, therefore, though absolutely larger, forms a smaller fraction of the whole cortex of the brain than in the lower forms. The statement that in the anthropoid (orang-outan) brain the groups of foci in the motor fields of the cortex are themselves separated one from another by surrounding inexcitable cortex, has been made and was one of great interest, but has not been confirmed by subsequent observat'on.