**Core Concept**
The carpometacarpal (CMC) joint of the thumb is a specialized joint that enables the unique range of motion and dexterity of the thumb. It is a type of saddle joint, characterized by a specific bony configuration that allows for opposition and circumduction movements.

**Why the Correct Answer is Right**
The CMC joint of the thumb is a saddle joint due to its unique bony structure. The joint is formed by the trapezium and the first metacarpal bone, which are shaped like a saddle and a post, respectively. This configuration allows for the intricate movements of the thumb, including opposition, flexion, extension, abduction, and adduction. The ligaments and muscles surrounding the joint provide additional stability and support for these movements.

**Why Each Wrong Option is Incorrect**
* **Option A:** The CMC joint is not a hinge joint, as it does not have the characteristic bony structure of a hinge joint, and it allows for more than just flexion and extension movements.
* **Option B:** The CMC joint is not a ball-and-socket joint, as it does not have the spherical shape of a ball-and-socket joint, and it does not allow for the same range of motion.

**Clinical Pearl / High-Yield Fact**
The CMC joint of the thumb is prone to osteoarthritis, particularly in women, due to repetitive strain and wear and tear. This can lead to pain, stiffness, and decreased dexterity in the thumb.

**Correct Answer: C. Saddle joint.**