What are the features and functions of the ball and socket joint, pelvic girdle, and associated bones like the atlas, axis, ilium, and pubis?

Here are the answers to your questions:

21.

a) Two features of a ball and socket joint are:

• It has a spherical head of one bone that fits into a cup-like socket of another bone.
• It allows for a wide range of motion including flexion, extension, abduction, adduction, rotation, and circumduction.

b) The bone that allows the head to:

i) node: Atlas

ii) turn side ways: Axis

22.
Two functions of the pelvic girdle in mammals are:

• It supports the weight of the upper body and transfers it to the lower limbs.
• It provides attachment points for muscles of the legs, trunk, and abdomen, and protects the organs within the pelvic cavity.

23.

a) How are the structures labelled H and J adapted to their function?

i) H (Ilium/Iliac crest): It is broad and flat to provide a large surface area for the attachment of powerful muscles of the trunk and legs, facilitating movement and support.

ii) J (Pubic symphysis): It is a cartilaginous joint that allows for slight flexibility and movement, which is crucial for widening the pelvic outlet during childbirth in females.

b) The function of the obturator foramen is to allow the passage of nerves and blood vessels (specifically the obturator nerve and vessels) to the thigh.

c)

i) The bone that articulates with the pelvic girdle at the acetabulum is the femur.

ii) The type of joint formed by the acetabulum and the femur is a ball and socket joint.