Saddle joints have concave and convex surfaces. Identify a saddle joint of the skeleton.

Choice A reason: Opposition is a specific movement that occurs primarily in the thumb. It refers to the ability of the thumb to touch the tips of the other fingers, allowing grasping and manipulation. This movement involves the thumb opposing the fingers, hence the term.

Choice B reason: False is incorrect because opposition is a well-defined movement in anatomy, particularly in the hand.

Choice A reason: The central canal, also known as the Haversian canal, is located at the center of each osteon in compact bone. It contains blood vessels and nerve fibers that supply nutrients and signals to the bone cells.

Choice B reason: Adipose tissue is found in yellow marrow, primarily in the medullary cavity of long bones, not in the central canal of osteons.

Choice C reason: Yellow marrow and spicules are found in the medullary cavity and spongy bone, respectively. They are not components of the central canal.

Choice D reason: Cartilage is not present in the central canal. Interstitial lamellae are layers of bone matrix found between osteons, not within the canal.

Choice E reason: Red marrow is found in spongy bone and certain flat bones, not in the central canal. While nerves are present, the absence of blood vessels in this choice makes it incomplete.