506. A disturbance in cartilage formation in a fetus results in deformities of theA disturbance in cartilage formation in a fetus results in deformities of the

1. sphenoid and zygomatic bones.

2. axial skeleton and the base of the skull.

3. axial skeleton and the flat bones of the skull.

4. petrous portion of the temporal bones and the parietal bones.



The correct answer is choice 2. Some bones in the human skeleton are formed by ossification of a cartilaginous model while others are not. When the bone is formed in a connective tissue other than cartilage, it is termed intramembranous ossification rather than cartilage ossification. Disturbance in cartilage formation will affect those bones produced on a cartilage model, but not those produced intramembranously. Let's check the choices. In general, the axial skeleton and skull base are ossified from cartilage models, so choice 2 is correct. Choice 3 is incorrect as most flat bones of the skull are intramembranous, not cartilaginous. Choice 4 is incorrect. The petrous portion of the temporal bone is from a cartilage model, while the squamous part is membranous. The parietal hones ossify intramembranously. Choice 1 is also incorrect. The sphenoid is mostly cartilaginous in ossification, but part of the greater wing is membranous. However, the zygomatic bone is intramembranous. So again the correct answer to question is choice 2.