Final answer:
The conus medullaris ends at the L1 and L2 vertebrae in adults, marking the transition from the spinal cord to the nerve roots of the cauda equina.
Step-by-step explanation:
The conus medullaris is the caudal end of the spinal cord, and in adults, it typically ends at the upper lumbar vertebral bones. Specifically, it is located around the level of the L1 and L2 vertebrae. At this point in the spinal column, the spinal cord terminates and gives way to a collection of nerve roots known as the cauda equina. These nerve roots extend downwards inside the vertebral column to reach their respective exit points at the intervertebral foramina. The spine's structure includes various regions corresponding to the different vertebrae, namely cervical (C1-C7), thoracic (T1-T12), and lumbar (L1-L5) vertebrae, and the conus medullaris marks the transition from the spinal cord to the nerve roots.