**Core Concept**
The axillary lymph nodes are divided into five groups based on their location and function: pectoral, humeral, axillary, subscapular, and apical. The terminal group of lymph nodes refers to the final group of nodes through which lymph flows before it enters the bloodstream.

**Why the Correct Answer is Right**
The apical group of axillary lymph nodes is the terminal group, as it receives lymph from all other axillary lymph nodes and drains into the subclavian lymphatic trunk. This group is located at the apex of the axilla, near the axillary vein. The apical nodes are also the first point of drainage for the breast and are often involved in breast cancer metastasis.

**Why Each Wrong Option is Incorrect**
* **Option A:** The pectoral group of lymph nodes is not the terminal group, as it receives lymph from the anterior chest wall and breast, but not from the other axillary nodes.
* **Option B:** The humeral group of lymph nodes is not the terminal group, as it receives lymph from the upper arm and forearm, but not from the other axillary nodes.
* **Option C:** The subscapular group of lymph nodes is not the terminal group, as it receives lymph from the posterior chest wall and scapular region, but not from the other axillary nodes.

**Clinical Pearl / High-Yield Fact**
Remember that the apical group of axillary lymph nodes is the most common site for breast cancer metastasis, making it an important node to evaluate in breast cancer staging.

**Correct Answer:** C.