Final answer:
The prefix quadri- in the term quadriceps indicates the number four, referring to the four muscles that comprise the quadriceps femoris group in the thigh.
Step-by-step explanation:
In the term quadriceps, the prefix quadri- refers to the number four. Specifically, it indicates that the quadriceps femoris group is composed of four muscles. These muscles, located in the anterior compartment of the thigh, work together to extend and stabilize the knee. The quadriceps femoris group includes the rectus femoris, vastus lateralis, vastus medius, and vastus intermedius. These muscles are activated during the extension of the knee, acting as the agonists of knee extension, and they all share a common insertion via the quadriceps tendon into the patella.