What is the primary characteristic of the human lumbar vertebrae?

The primary characteristic of the human lumbar vertebrae is that they are larger and sturdier compared to the vertebrae in other regions of the spine. This increased size and robustness allow the lumbar vertebrae to support the weight of the upper body and maintain stability while also allowing for a limited range of movement. The lumbar region is specifically designed to bear significant loads and provide structural support during activities such as lifting and bending, which is essential for overall spinal integrity and function.

In contrast, fused vertebrae are typically found in the sacral and coccygeal regions rather than the lumbar area. The unique curvature, while relevant to the spinal structure as a whole, does not specifically distinguish the lumbar vertebrae. Additionally, while the number of lumbar vertebrae (usually five) is fewer than that of the cervical vertebrae (seven), the distinction here lies in their size and function rather than in their numerical quantity. Thus, the defining feature of the lumbar vertebrae is indeed their larger and sturdier nature, making option B the correct choice.