**Core Concept**
Rotter's nodes are a group of lymph nodes in the axillary region that play a crucial role in the drainage of the breast and chest wall. They are located in the axilla, specifically in the lower border of the pectoralis minor muscle.

**Why the Correct Answer is Right**
The correct answer is related to the anatomical location of Rotter's nodes. These nodes are situated in the axillary region, and their position is critical for understanding the spread of breast cancer and other conditions affecting the chest wall. The pectoralis minor muscle acts as a landmark for identifying Rotter's nodes, which are located below its lower border. This anatomical position facilitates the drainage of lymph from the breast and chest wall into the axillary lymph nodes.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option does not specify a correct location for Rotter's nodes. Without a clear location, it is difficult to determine the accuracy of this option.
* **Option B:** This option may refer to another group of lymph nodes, but it does not accurately describe the location of Rotter's nodes. Without more information, it is challenging to evaluate the validity of this option.
* **Option C:** This option is not a recognized location for Rotter's nodes. It may be a distractor intended to confuse the test-taker.

**Clinical Pearl / High-Yield Fact**
Rotter's nodes are an important landmark in breast cancer staging and treatment. Knowledge of their location is crucial for surgeons and radiologists to accurately assess the extent of disease spread and plan appropriate treatment.

**Correct Answer: C. In the lower border of the pectoralis minor muscle.**