Which group of bones are not movable portion of skull ?

Question

Accepted Answer

The correct option is (4):
The correct option is Maxilla, Frontal Bone and Zygomatic Bone. This group consists entirely of bones that are fixed, or *not movable*, portions of the skull. The Maxilla, which forms the upper jaw and part of the nasal cavity and eye orbits, the Frontal Bone, which constitutes the forehead, and the Zygomatic Bone, which is the cheekbone, are all securely joined to adjacent bones by fibrous joints known as sutures. These sutures are immovable joints (synarthroses) in an adult skull, designed to provide rigid protection for the brain and stability for the face. The foundational principle here is that, with one crucial exception, all bones of the skull are immovable.

The incorrect option is (1):
The option Mandible, Maxilla and Frontal Bone is incorrect because it includes the **Mandible**. The Mandible is the lower jawbone and is the single, key exception to the rule of fixed skull bones, as it is highly movable. It articulates with the temporal bone at the complex temporomandibular joint (TMJ), enabling the essential movements of the jaw like chewing, speaking, and yawning. Although the Maxilla and Frontal Bone are non-movable, the Mandible's mobility makes this group an incorrect answer to the question.

The incorrect option is (2):
The option Mandible, Frontal Bone and Zygomatic Bone is also incorrect due to the inclusion of the **Mandible**. The lower jawbone's ability to move is vital for human function and is achieved through the only freely movable joint in the skull—the temporomandibular joint. In contrast, the Frontal Bone, located in the cranium, and the Zygomatic Bone, which helps form the mid-face, are both fixed bones. A group that contains the Mandible cannot be described as a group of *not movable* skull bones.

The incorrect option is (3):
The option Zygomatic Bone, Mandible and Maxilla is incorrect because of the presence of the **Mandible**. While both the Zygomatic Bone (cheekbone) and the Maxilla (upper jaw) are stable bones that contribute to the facial structure and are fixed by tight sutures, the Mandible is the mobile element. Its unique articulation and range of motion for functions like mastication and speech distinguish it from the rigidly fused bones listed alongside it, thus failing to meet the criteria of a completely non-movable group.