Good day everyone, Today we are going to discuss fully on appendicular skeleton;
Learning outcomes
After studying this section, you should be able to:
- identify the bones forming the appendicular skeleton
- state the characteristics of the bones forming the appendicular skeleton
- outline the differences in structure between the male and female pelves.
The appendicular skeleton consists of the:
- pelvic girdle with the lower limbs.
- shoulder girdle with the upper limbs
Shoulder girdle and upper limb
The upper limb forms a joint with the trunk via the shoulder (pectoral) girdle.
Also read: Axial skeleton
Shoulder girdle
The shoulder girdle consists of two clavicles and two scapulae.
Clavicle (collar bone)
The clavicle is an S-shaped long bone. It articulates with the manubrium of the sternum at the sternoclavicular joint and forms the acromioclavicular joint with the acromion process of the scapula. The clavicle provides the only bony link between the upper limb and the axial skeleton.
Also read: obstructive lung disorder
Scapula (shoulder blade)
The scapula is a flat triangular-shaped bone, lying on the posterior chest wall superficial to the ribs and separated from them by muscles.
At the lateral angle is a shallow articular surface, the glenoid cavity, which, with the head of the humerus, forms the shoulder joint.
On the posterior surface runs a rough ridge called the spine, which extends beyond the lateral border of the scapula and overhangs the glenoid cavity. The prominent overhang, which can be felt through the skin as the highest point of the shoulder, is called the acromion process and forms a joint with the clavicle, the acromioclavicular joint, a slightly movable synovial joint that contributes to the mobility of the shoulder girdle. The coracoid process, a projection from the upper border of the bone, gives attachment to muscles that move the shoulder joint.
The upper limb
Humerus
This is the bone of the upper arm. The head sits within the glenoid cavity of the scapula, forming the shoulder joint. Distal to the head are two roughened projections of bone, the greater and lesser tubercles, and between them there is a deep groove, the bicipital groove or intertubercular sulcus, occupied by one of the tendons of the biceps muscle.
The distal end of the bone presents two surfaces that articulate with the radius and ulna to form the elbow joint.
Ulna and radius
These are the two bones of the forearm. The ulna is longer than and medial to the radius and when the arm is in the anatomical position, i.e. with the palm of the hand facing forward, the two bones are parallel. They articulate with the humerus at the elbow joint, the carpal bones at the wrist joint and with each other at the proximal and distal radioulnar joints. In addition, an interosseous membrane, a fibrous joint, connects the bones along their shafts, stabilising their association and maintaining their relative positions despite forces applied from the elbow or wrist.
Carpal (wrist) bones
There are eight carpal bones arranged in two rows of four. From outside inwards they are:
- proximal row: scaphoid, lunate, triquetrum, pisiform
- distal row: trapezium, trapezoid, capitate, hamate.
These bones are closely fitted together and held in position by ligaments that allow a limited amount of movement between them. The bones of the proximal row are associated with the wrist joint and those of the distal row form joints with the metacarpal bones. Tendons of muscles lying in the forearm cross the wrist and are held close to the bones by strong fibrous bands, called retinacula.
Metacarpal bones (bones of the hand)
These five bones form the palm of the hand. They are numbered from the thumb side inwards. The proximal ends articulate with the carpal bones and the distal ends with the phalanges.
Phalanges (finger bones)
There are 14 phalanges, three in each finger and two in the thumb. They articulate with the metacarpal bones and with each other, by hinge joints.
Pelvic girdle and lower limb
The lower limb forms a joint with the trunk at the pelvic girdle.
The pelvic girdle
The pelvic girdle is formed from two innominate (hip) bones. The pelvis is the term given to the basin-shaped structure formed by the pelvic girdle and its associated sacrum.
Innominate (hip) bones
Each hip bone consists of three fused bones: the ilium, ischium and pubis. On its lateral surface is a deep depression, the acetabulum, which forms the hip joint with the almost-spherical head of femur.
The ilium is the upper flattened part of the bone and it presents the iliac crest, the anterior curve of which is called the anterior superior iliac spine. The ilium forms a synovial joint with the sacrum, the sacroiliac joint, a strong joint capable of absorbing the stresses of weight bearing and which tends to become fibrosed in later life.
The pubis is the anterior part of the bone and it articulates with the pubis of the other hip bone at a cartilaginous joint, the symphysis pubis.
The ischium is the inferior and posterior part. The rough inferior projections of the ischia, the ischial tuberosities, bear the weight of the body when seated.
The union of the three parts takes place in the acetabulum.
The pelvis
The pelvis is formed by the hip bones, the sacrum and the coccyx. It is divided into upper and lower parts by the brim of the pelvis, consisting of the promontory of the sacrum and the iliopectineal lines of the innominate bones.
Differences between male and female pelves
The shape of the female pelvis allows for the passage of the baby during childbirth. In comparison with the male pelvis, the female pelvis has lighter bones, is more shallow and rounded and is generally roomier.
