What is the correct number of cervical, thoracic, lumbar, and sacral vertebrae respectively?

Choice A reason: A meatus is a canal-like passageway through bone, such as the external auditory meatus. It does not describe a projection and is not involved in articulation.

Choice B reason: A fossa is a shallow depression in a bone, often serving as a site for muscle attachment or articulation. However, it is not a projection but rather a concavity.

Choice C reason: An epicondyle is a raised area on or above a condyle, typically serving as a site for muscle attachment. While it is a projection, it is not the rounded articular type described in the question.

Choice D reason: A condyle is a rounded articular projection that typically forms part of a joint. It allows for smooth articulation with another bone and is the correct term for the structure described.

Choice E reason: A foramen is a hole or opening in a bone that allows the passage of nerves and blood vessels. It is not a projection and does not serve an articulating function.

Choice A reason: Hinge joints allow movement in one plane, such as flexion and extension. Examples include the elbow and knee, but the joint between the radius and ulna does not function this way.

Choice B reason: This is correct. The proximal radioulnar joint is a pivot joint, allowing rotational movement such as pronation and supination of the forearm. The radius rotates around the ulna, enabling the palm to turn up or down.

Choice C reason: Plane or gliding joints allow sliding movements between flat surfaces, such as those between carpal bones. This does not apply to the radius and ulna.

Choice D reason: Saddle joints allow movement in two planes and are found in the thumb (carpometacarpal joint). The radius and ulna do not form a saddle joint.

Choice E reason: Ball-and-socket joints allow movement in multiple directions and are found in the shoulder and hip. The radius and ulna do not form this type of joint.