Final answer:
The buccinator muscle compresses the cheeks inward and is essential for actions like blowing, sucking, and chewing.
Step-by-step explanation:
The muscle that compresses the cheeks inward when it contracts is the buccinator muscle.
This muscle plays a crucial role in facial expressions and functions such as blowing, sucking, and chewing.
While there are many muscles involved in the facial expressions, the buccinator is specifically responsible for the lateral movement of the cheeks, as for example, when you suck on a straw.