**Core Concept:** Intramembranous ossification is a process of bone formation where osteoblasts differentiate directly from mesenchymal cells, without the involvement of endochondral ossification pathway (formation of cartilage first). Intramembranous ossification occurs in flat bones, small bones of the skull, scapulae, and clavicles.

**Why the Correct Answer is Right:** Intramembranous ossification is characterized by direct differentiation of mesenchymal cells into osteoblasts, which form bone tissue. This process occurs in specific bones where endochondral ossification may not be suitable due to their thin and flat structure. The four bones mentioned in the options are all examples of such bones where intramembranous ossification takes place.

**Why Each Wrong Option is Incorrect:**

A. Intramembranous ossification does occur in long bones like the radius and ulna, but not in the bones of the lower limbs, which undergo endochondral ossification.

B. Intramembranous ossification is not limited to the bones of the skull and face, as it also occurs in the scapulae (shoulder blades) and clavicles (collar bones).

C. Although some bones in the limbs undergo intramembranous ossification, it is less common compared to endochondral ossification, and therefore, it is not a primary characteristic of limb bones.

D. Intramembranous ossification is not limited to the bones of the skull and face, as it also occurs in the scapulae (shoulder blades) and clavicles (collar bones).

**Clinical Pearl:** Intramembranous ossification is essential to understand for students of Anatomy, Orthopedics, and Radiology. It enables them to identify and differentiate between the types of ossification processes used in different skeletal elements, especially in the skull, scapulae, and clavicles.

**Correct Answer:** D. Intramembranous ossification is not limited to the bones of the skull and face, as it also occurs in the scapulae (shoulder blades) and clavicles (collar bones).

**Explanation:** Intramembranous ossification is a crucial concept in understanding bone development and differentiation. It involves the direct formation of bone tissue from mesenchymal cells without the formation of cartilage first. The process primarily occurs in bones that need to be thin, flat, and lightweight, making the answer D the correct choice. Additionally, the other options are incorrect because they either overemphasize the role of intramembranous ossification in limb bones or do not mention the scapulae and clavicles as examples of bones formed by intramembranous ossification.