Final answer:
Broca's area is the part of the frontal lobe that controls language expression by directing muscle movements involved in speech, usually located in the brain's left hemisphere.
Step-by-step explanation:
The area of the frontal lobe that is responsible for language expression by directing the muscle movements involved in speech is known as Broca's area. This region is associated with the motor commands necessary for speech production and is typically found in the left hemisphere of the brain, which is responsible for language production in about 95% of people. Broca's area is located adjacent to the motor cortex which controls bodily movements and is specifically involved in controlling the movements that are crucial for articulate speech.