Step 1: Understanding the Concept
Posture and muscle tone are controlled by extrapyramidal motor pathways.
Step 2: Red nucleus
The red nucleus in the midbrain receives input from the cerebellum and cerebrum and adjusts muscle tone and posture.
Step 3: Compare the options
The pons acts as a relay and breathing centre, crura cerebri are fibre tracts, and the thalamus relays sensory impulses.
Final Answer:
The red nucleus controls posture and muscle tone.
\[ \boxed{\text{(B) }\text{Red nucleus}} \]