Connective tissue sacs lined with synovial membrane that act as cushions in places where friction develops are called:

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: Circumduction is a circular movement that combines flexion, extension, abduction, and adduction. It is typically seen in ball-and-socket joints like the shoulder or hip, not in the neck. It does not describe the backward bending of the head.

Choice B reason: Rotation refers to the movement of a bone around its longitudinal axis, such as turning the head side to side. It does not involve bending the head backward.

Choice C reason: Hyperextension occurs when a joint is extended beyond its normal anatomical position. In the case of the head, bending it backward past the neutral anatomical position is a classic example of hyperextension.

Choice D reason: Flexion is the movement that decreases the angle between two body parts, such as bending the head forward toward the chest. It is the opposite of the movement described in the question.