Which of the following bones has no medullary cavity?
**Core Concept**
The medullary cavity is a hollow, spongy space within the shaft of long bones, filled with bone marrow. It serves as a site for hematopoiesis and energy storage. The presence or absence of a medullary cavity is a characteristic feature of different bones.
**Why the Correct Answer is Right**
The bones without a medullary cavity are typically short, flat, or irregular bones. These bones have a solid, dense structure that does not accommodate a medullary cavity. The absence of a medullary cavity in these bones is due to their compact, cancellous bone structure, which does not require a space for marrow or energy storage.
**Why Each Wrong Option is Incorrect**
**Option A:** The femur, being a long bone, has a well-defined medullary cavity.
**Option B:** The humerus, another long bone, also possesses a medullary cavity.
**Option C:** The pelvis, a complex, irregular bone, contains a medullary cavity in some of its components, such as the ilium.
**Clinical Pearl / High-Yield Fact**
Keep in mind that the absence of a medullary cavity is a characteristic feature of short, flat, or irregular bones, which often have a compact, cancellous bone structure.
**Correct Answer:** C.