Final answer:
The inferior nasal concha is the concha not directly attached to the ethmoid bone; it is an independent bone of the skull and the largest of the nasal conchae.
Step-by-step explanation:
In the nasal cavity of the skull, there are three nasal conchae: the superior, middle, and inferior. The superior nasal concha and middle nasal concha are both parts of the ethmoid bone, a key component in the lateral walls of the nasal cavity.
In contrast, the inferior nasal concha is a separate, independent bone and does not attach directly to the ethmoid bone. This distinct characteristic makes the inferior nasal concha the largest and most easily visible when looking into the anterior opening of the nasal cavity. Therefore, the concha that is not a direct attachment of the ethmoid bone is the inferior nasal concha.