**Core Concept**
The cubital fossa is a triangular area in the anterior view of the elbow joint, bordered by three distinct anatomical structures. In this context, we are focusing on the lateral boundary, which is a key aspect of elbow anatomy.

**Why the Correct Answer is Right**
The lateral boundary of the cubital fossa is formed by the **Brachioradialis muscle**. This muscle is a forearm flexor that runs from the humerus to the radius bone. Its position and orientation make it the lateral landmark of the cubital fossa. When the elbow is flexed, the brachioradialis muscle becomes more prominent, forming the lateral border of the cubital fossa.

**Why Each Wrong Option is Incorrect**
**Option A:** Brachialis is not the lateral boundary, but rather a flexor of the elbow that lies deeper in the cubital fossa.
**Option B:** Pronator teres is a muscle involved in forearm pronation, but it is not the lateral boundary of the cubital fossa.
**Option C:** Biceps is a muscle that forms part of the medial boundary of the cubital fossa, not the lateral one.

**Clinical Pearl / High-Yield Fact**
To remember the boundaries of the cubital fossa, use the mnemonic "BNB": Biceps (medial), Nerve (median nerve), and Brachioradialis (lateral).

**✓ Correct Answer: A. Brachioradialis**