Final answer:
The lateral horn of the spinal cord is located in the gray matter between T1 and L2, part of the thoracolumbar system serving the sympathetic division of the autonomic nervous system.
Step-by-step explanation:
The lateral horn, also known as the accessory horn, of the spinal cord is a region within the gray matter and is crucial for the autonomic nervous system, specifically the sympathetic division. This structure is not distributed evenly along the length of the spinal cord but is instead located exclusively within certain spinal cord segments. Based on the information provided, the lateral horn is found in the thoracic, upper lumbar, and sacral regions of the spinal cord. These regions correspond to spinal cord segments from T1 through L2 and sacral segments, which align best with the anatomical area known as the thoracolumbar system.
Given the options presented in the question, the correct answer is: b) Only between T1-L2. The lateral horn is thus an integral part of the thoracolumbar system serving the sympathetic division of the autonomic nervous system.