**Core Concept**
The quadrangular space, also known as the quadrilateral space, is a narrow anatomical passage in the shoulder region that provides a pathway for the axillary nerve and the posterior circumflex humeral artery. It is situated under the deltoid muscle and is bounded by four key structures.

**Why the Correct Answer is Right**
The long head of the biceps brachii muscle does not form a boundary of the quadrangular space. The correct boundaries of the quadrangular space are:
- Teres minor (Option A) - the posterior wall of the space
- Teres major (Option B) - the medial wall of the space
- Surgical neck of humerus (Option C) - the superior wall of the space
- Long head of triceps brachii (not listed) - the inferior wall of the space, not the long head of biceps brachii

**Why Each Wrong Option is Incorrect**
**Option A:** Teres minor does form a boundary of the quadrangular space, serving as the posterior wall.
**Option B:** Teres major does indeed form a boundary, acting as the medial wall.
**Option C:** The surgical neck of the humerus is a correct boundary, forming the superior wall of the quadrangular space.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the quadrangular space is a significant anatomical landmark for surgeons, as it is a common pathway for neurovascular structures, including the axillary nerve and the posterior circumflex humeral artery. Injury to these structures within the quadrangular space can result in significant morbidity.

**✓ Correct Answer: D. Long head of biceps brachii**