The vertebral column, also called the backbone, is made up of 33 vertebrae that are separated by spongy disks and classified into four distinct areas. The cervical area consists of seven bony parts in the neck; the thoracic spine consists of 12 bony parts in the back area; the lumbar spine consists of five bony segments in the lower back area; five sacral* bones; and four coccygeal* bones (the number of coccygeal bones can vary from five to three).
(* By adulthood, the 5 sacral vertebrae fuse to form one bone, and the 4 coccygeal vertebrae fuse to form one bone.)
The pelvis is a basin-shaped structure that supports the spinal column and protects the abdominal organs. It contains the following:
sacrum - a spade-shaped bone that is formed by the fusion of five originally separate sacral vertebrae.
coccyx (Also called the tail bone.) - formed by the fusion of four originally separated coccygeal bones.
three pelvic (hip) bones, including the following:
ilium - the broad, flaring portion of the pelvis.
pubis - the lower, posterior part of the pelvis.
ischium - part of the pelvis that forms the hip joint.
The shoulder is made up of several layers, including the following:
bones - the collarbone (clavicle), the shoulder blade (scapula), and the upper arm bone (humerus).
joints - facilitate movement, including the following:
sternoclavicular joint (where the clavicle meets the sternum)
acromioclavicular (AC) joint (where the clavicle meets the acromion)
shoulder joint (glenohumeral joint) - a ball-and-socket joint that facilitates forward, circular, and backward movement of the shoulder.
ligaments - a white, shiny, flexible band of fibrous tissue that binds joints together and connects various bones and cartilage, including the following:
joint capsule - a group of ligaments that connects the humerus to the socket of the shoulder joint on the scapula to stabilize the shoulder and keep it from dislocating.
ligaments that attach the clavicle to the acromion
ligaments that connect the clavicle to the scapula by attaching to the coracoid process
acromion - the roof (highest point) of the shoulder that is formed by a part of the scapula.
tendons - the tough cords of tissue that connect muscles to bones. The rotator cuff tendons are a group of tendons that connect the deepest layer of muscles to the humerus.
muscles (to help support and rotate the shoulder in many directions)
bursa - a closed space between two moving surfaces that has a small amount of lubricating fluid inside; located between the rotator cuff muscle layer and the outer layer of large, bulky muscles.
rotator cuff - composed of tendons, the rotator cuff (and associated muscles) holds the ball of the glenohumeral joint at the top of the upper arm bone (humerus).