Skeletal System: Bones and joints form the skeletal system of the body.  Bones provides a framework which protects and supports internal organs. They also provide attachments to the muscles. Because of the contraction of the muscles mobility is possible. The inner core of the bone consists of bone marrow where blood cells are manufactured.

Bones of the skeletal are classified as:

  1. Long bones: They are found in the thigh and the upper arm. A long bone contains a shaft and two extremities. The shaft is known as diaphysis and the extremities are known as epiphysis.
  2. Short Bones: These bones have no shaft. But they contain a spongy substance covered by shell of compact bone e.g. small bones of wrist and ankle.
  3. Flat Bones: They contain two layers of compact bone with a spongy substance in between e.g. pelvic bones and scapula.
  4. Sesamoid bones: These are small bones which develop in the tendons of muscles e.g. patella of knee joint.

Structure of Bone: Bone is the hardest of the connective tissues. It consists of two kinds of connective tissues.

  • Compact bone: It is hard and dense. It is found in flat bones, in the shafts of long bones and as a thin covering of all bones.
  • Cancellous bones: It is spongy in appearance. It is found in the ends of long bones, in short bones and in between two layers of compact tissue of flat bones. 

Gross structure of a long bone: A long bone has two ends (epiphysis) connected by a shaft (diaphysis). The outer membrane covering the bone is periostem. It is followed by a thick layer of compact bone. Inside this is a central medullary canal. Nutrient foramen is the opening through which arteries pierce the medullay canal.


Formation of the bones is called OSSIFICATION. Bones of the skeleton are developed in two ways:

  1. Some bones develop in sheets of fibrous tissue (intra-membranous ossification).
  2. Other bones develop in bars of cartilage (intra-cartilaginous ossification).

In both cases, bone cells called osteoblast invade the area of ossification. Here, calcium salts are deposited to give the necessary hardness. This process of bone development occurs before birth. After birth, the bone grows from certain centers in it. The centre in the shaft is called diaphysis. The two centers in the ends are called epiphysis. The layer of cartilage in between the epiphysis and diaphysis is called epiphyseal cartilage or growth plate. This is form a single bony structure.  After this, the growth of bone stops. Osteoclasts are bone phagocytes which help in reabsorption of bone and bone remodeling.

A total of 206 bones form the human skeleton. These bones can be classified as:

  1. Bones of the skull: Bones of cranium, face, and lower jaw.
  2. Bones of the trunk: Ribs, sternum, and vertebral column.
  3. Bones of upper limb: Scapula (shoulder girdle, humerus (arm bone), radius, and ulna (forearm bones).
  4. Bones of lower limbs: Pelvic girdle (hip bone), femur (thigh bone), tibia, fibula (leg bones), and, metatarsal bones (foot bones).

Bones of the skull and trunk form the axial skeleton. Bones of the upper and lower limbs form the appendicular skeleton.
Bones of the skull are divided into two groups:

  1. Bones of cranium (or brain box).
  2. Bones of face.

Bones of cranium
Cranium is formed by 8 bones. They are:

  1. One frontal bone.
  2. Two parietal bones.
  3. Two temporal bones.
  4. One occipital bone.
  5. One sphenoid bone.
  6. One ethmoid bone.
  • Frontal bone: It forms the forehead and the roof of the orbit.
  • Parietal bones: They are two in number. Both form the roof and upper part of the sides of the skull.
  • Temporal bones: They are two in number. They form the lower part of the sides of the skull.
  • Occipital bone: It is at the back and lower part of the cranial cavity and joins parietal and temporal bones.
  • Sphenoid bone: It lies at ehe base of the skull. It form a large part of middle cranial fossa. It is bat shaped bone attached to frontal, occipital and ethmoid bones.
  • Ethmoid bone:  It is cubical in shape. It is very delicate and thin. It is situated at the roof of nose and in between the orbits.

Sutures of the cranium: Sutures are the immovable joints which unite the bones of skull. The important sutures are:

  1. Coronal suture: Between the frontal bone and the two parietal bones.
  2. Sagittal suture: Between the two parietal bones.
  3. Lambdoid suture: Between the occipital bone and the two parietal bones.

The fontanelle: At birth, skull bones of the child are not completely ossified. The space between the bones is filled by membranes. These membranes at the angles of bones are called fontanelles. These fontanelles are:

  1. Anterior fontanel: It is the largest of the fontanelle. It is situated at the junction of frontal and two parietal bones. Here, the coronal and sagittal sutures meet. This fontanelle closes at the age of 1year and 6 months.
  1. Posterior fontanel: It is at the back. It occurs at the junction of two parietal and the occipital bones. It closes soon after birth.

Sinuses of the skull: These are cavities or chambers present in the bones of the skull. The four important sinuses are:

  1. Frontal sinus: They are two in number present in the frontal bones. They are present on each side at the roof of the nose.
  2. Maxillary sinuses: Two in number present in the maxillary bones. They lie on each side of the nose.
  3. Ethmoid and sphenoid sinuses: They are the outer sinuses present in skull.

The bones which make the face are 14 in number. These bones are:

  1. Two maxillae (upper jaw).
  2. One mandible (lower jaw).
  3. Two Palate bones.
  4. Two zygomatic bones.
  5. Two lacrimal bones.
  6. Two nasal bones.
  7. Two inferior turbinate bones.
  8. One vomer.
  • Maxillae: They are two in number. These bones form the upper jaw.
  • Mandible: This bone forms the lower jaw and is the only movable bone of the skull.    Temporomandibular joint is formed by the articulation of condyle of the mandible with the temporal bone.
  • Palate bones: They are two in number. They form the roof of the oral cavity and the hard palate.
  • Zygomatic bones: Two bones. They form a part of the floor of the orbit.
  • Lacrimal bones: They are two bones found in the interior of the orbit. It contains the lacrimal sac, which secretes the lacrimal fluid.
  • Nasal bones: They are two in number. They form the nasal bridge.
  • Inferior turbinate bones: Two in number. They are also called as nasal conchae. They are found in the interior of the nasal cavity.
  • Vomer: It is a V-shaped bone. It is located in the midsagittal line, and touches the sphenoid, the ethmoid, the left and right palatine bones, and the left and right maxillary bones. 


  • Scapula: It lies at the back of the thorax. It forms the posterior part of the shoulder girdle.
  • Clavicle: It is also called collarbone. It forms the anterior part of shoulder girdle.
  • Humerus: It is the longest bone of upper limb. It contains two extremities and shaft.
  • Ulna: It is inner most bone of the forearm.
  • Radius: it is the lateral or outermost bone of forearm.


Bones of wrist: The bones of carpus or wrist are arranged in two rows.

First or proximal row made of scaphoid, lunate, triquetrum, and pisiform bones.

Second or distal row made of trapezium, trapezoid, capitate, and hamate bones.

Bones of palm: They are made of metacarpal bones. They are long bones which contain a head, a shaft and a base. The bases articulate with the distal row of carpal bones. The heads articulate with the proximal row of phalanges.

Bones of fingers: They are made of phalangeal bones. These are long bones. The thumb has two phalanges. Other fingers have three phalanges. They are proximal, Middle and distal phalanges.

Metacarpo-phalangeal joints (MCPJoints) are the joints between metacarpal and phalangeal bones.
Interphalangeal joints (IPJoints) are the joints between the phalangeal bones themselves.

The skeleton of the thorax is made up of the following bones

  1. Sternum in the front.
  2. twelve pairs of ribs at the sides.
  3. Twelve thoracic vertebrae at the back.

Sternum: It is also called breast bone. It is a flat bone which is divided into three parts- namely manubrium sterni, body of sternum, and xiphoid bone.

Manubrium sterni: It is the upper part, which is triangular in shape. It contains:

  1. Clavicular notches on both sides. These notches articulate with clavicle.
  2. Suprasternal notch which is present in between the two clavicular notches.
  3. Articular surface on both sides for the first rib.

Body of sternum (Gladiolus): The second rib is attached at the junction between manubrium sterni and body of sternum. This junction is called Angle of Ludwig. The body of sternum has attachments for 3rd, 4th, 5th, 6th and 7th ribs.

Xiphoid bone (Ensiform process): It lies in the lowest part of sternum. 

They are arranges in twelve pairs. On the back side, all of them attached to thoracic vertebrae. Depending on their attachment in the front they are classified as:

  1. True ribs, which are the upper 1-7 pairs. They are attached to the sternum directly.
  2. False ribs, which are the lower three (8-10) pairs. They are attached to the sternum indirectly (Through costal cartilages).
  3. Floating ribs are the lowest two pairs. They are not attached in the front.

Vertebral column: The vertebral column (spinal column) is made of a number of bones. These bones are called vertebrae. In all, there are 33 vertebrae.

Classification of vertebrae: According to the region they occupy, the vertebrae are classified as:

  1. Cervical vertebrae: 7 in number. They form the neck region.
  2. Thoracic vertebrae: 12 in number. They for the back of thorax.
  3. Lumber vertebrae: 5 in number. They form the lumbar region.
  4. Sacral vertebrae: 5 in number. They are fused and form the sacrum.
  5. Coccygeal vertebrae: 4 in number. They are fused and form coccyx or tail bone.

Except the first and the second cervical vertebrate (axis and atlas), the other vertebrate have similar characteristics. So these other vertebrae are called typical vertebrae. In between the vertebrae, intervertebral space is present which is filled by fibrocartilage; this is known as intervertebral disc or disk.


The pelvic girdle is the connection between the trunk and lower extremities. It is formed by:

  1. Two innominate (without name) bones, one on each side.
  2. The sacrum and coccyx in between.

Nominate bone:  It is made of three parts namely ilium, ischium, and pubis. All these three bones unite to form large cup shaped cavity on the outer surface called acetabulum.

Ilium: It is upper expanded and flat part of innominate bone.

Pubis: It is the front portion of innominate bone.

Ischium: It is the solid, broad portion at the lower and back part of innominate bone. 


  • Femur: It is also called thighbone. It is the longest and strongest bone of the skeleton.
  • Patella: It is a sesamoid bone developed in the tendon of quadriceps femoris muscle.
  • Tibia: It is the innermost bone of the leg.
  • Fibula: It is the lateral or outermost bone of the leg. It is along and slender bone.

Bones of foot can be classified as:

  1. Tarsal bones (7 bones).
  2. Metatarsal bones (5 bones).
  3. Phalangeal bones (14 bones).
  • Tarsal bones: There are seven tarsal bones which includes:

the talus bone (articulates with leg bones)
the calcaneus bone (heel)
the three cuneiform bones
the cuboid bone
the navicular bone

  • Calcaneum: It is the largest bone of the foot. It lies at the back of the foot. Above, it articulates with talus and in front with cuboid.
  • Talus: The talus is the second largest of the tarsal bones. It forms the central and highest point of foot. It articulates at the sides with medial  and lateral malleoli and below with calcaneum.
  • Navicular (or scaphoid): It is a disc-shaped bone. It is present in the medial aspect of foot. It lies between talus at the back and three cuneiform bones in front.
  • Cuboid: It is in the lateral aspect of foot. Behind, it articulates with calcaneum. In front, it articulates with two lateral metatarsal bones.
  • Cuneiform bones: They are three in number namely medical, intermediate and lateral cuneiform bones. Posteriorly they articulate with navicular bone. Anteriorly they articulate with three metatarsal bones. 

Metatarsal bones: They are five in number. They correspond with the five toes. All of them are long bones.

Phalanges: They are 14 bones, two for the first toe and tree of the rest.

Differences between males and females:
Males and females have slightly different skeletons, including a different elbow angle. Males have slightly thicker and longer legs and arms; females have a wider pelvis and a larger space within the pelvis, through which babies travel when they are born.

The movements at joints:
Flexion: Movements increasing the angle between two bones.
Extension: Movements decreasing the angle between two bones.
Abduction: Movement of a body part away from the median plane of the body.
Adduction: Movement of a body part toward the median plane of the body.
Rotation: Circular movement around an axis.
Dorsiflexion: Upward movement (extension) of the foot or toes or of the hand or fingers.
Plantar flexion: bending the foot or toes toward the plantar surface.
Supination (Applied to arm): Turning the palm upwards.
Pronation (Applied to arm): Turning the palm downwards.

A joint is the location at which two or more bones make contact.  They are constructed to allow movement and provide mechanical support, and are classified structurally and functionally.
Synovial joints (or diarthroses, or diarthroidal joints) are the most common and most moveable type of joints in the body. As with all other joints in the body, synovial joints achieve movement at the point of contact of the articulating bones. Structural and functional differences distinguish the synovial joints from the two other types of joints in the body, with the main structural difference being the existence of a cavity between the articulating bones and the occupation of a fluid in that cavity which aids movement.

  1. Ball and socket joints, such as the shoulder and hip joints. These allow a wide range of movement.
  2. Condyloid joints (or ellipsoidal joints), such as the wrist. A condyloid joint is where two bones fit together with an odd shape (e.g. an ellipse), and one bone is concave, the other convex. Some classifications make a distinction between condyloid and ellipsoid joints.
  3. Saddle joints, such as at the thumb (between the metacarpal and carpal). Saddle joints, which resemble a saddle, permit the same movements as the condyloid joints.
  4. Hinge joints, such as the elbow (between the humerus and the ulna). These joints act like a door hinge, allowing flexion and extension in just one plane.
  5. Pivot joints, such as the elbow (between the radius and the ulna). This is where one bone rotates about another.
  6. Gliding joints (or planar joints), such as in the carpals of the wrist. These joints allow a wide variety of movement, but not much distance. they provide a full variety of movement.



Cardiac muscle tissue forms the bulk of the wall of the heart. Like skeletal muscle tissue, it is striated (the muscle fibers contain alternating light and dark bands (striations) that are perpendicular to the long axes of the fibers). Unlike skeletal muscle tissue, its contraction is usually not under conscious control (involuntary).


Smooth muscle tissue is located in the walls of hollow internal structures such as blood vessels, the stomach, intestines, and urinary bladder. Smooth muscle fibers are usually involuntary, and they are nonstriated (smooth). Smooth muscle tissue, like skeletal and cardiac muscle tissue, can undergo hypertrophy. In addition, certain smooth muscle fibres, such as those in the uterus, retain their capacity for division and can grow by hyperplasia.


Skeletal muscle tissue is named for its location – attached to bones. It is striated; that is, the fibers (cells) contain alternating light and dark bands (striations) that are perpendicular to the long axes of the fibers. Skeletal muscle tissue can be made to contract or relax by conscious control (voluntary).
Muscles in the alphabetical order
A – E
 abductor digiti minimi (in the hand), abductor digiti minimi (in the foot), abductor hallucis, abductor ossis metatarsi quinti, abductor pollicis brevis, abductor pollicis longus, adductor brevis, adductor hallucis, adductor longus, adductor magnus, adductor pollicis, anconeus, anterior scalene, articularis genus, biceps brachii, biceps femoris, brachialis, brachioradialis, buccinator, coracobrachialis, corrugator supercilii, deltoid, depressor anguli oris, depressor labii inferioris, digastric, dorsal interossei (in the hand), dorsal interossei (in the foot), extensor carpi radialis brevis, extensor carpi radialis longus, extensor carpi ulnaris, extensor digiti minimi, extensor digitorum, extensor digitorum brevis, extensor digitorum longus, extensor hallucis brevis, extensor hallucis longus, extensor indicis, extensor pollicis brevis, extensor pollicis longus

 F – L
 flexor carpi radialis, flexor carpi ulnaris, flexor digiti minimi brevis (in the hand), flexor digiti minimi brevis (in the foot), flexor digitorum brevis, flexor digitorum longus, flexor digitorum profundus, flexor digitorum superficialis, flexor hallucis brevis, flexor hallucis longus, flexor pollicis brevis, flexor pollicis longus, frontalis, gastrocnemius, geniohyoid, gluteus maximus, gluteus medius, gluteus minimus, gracilis, iliocostalis cervicis, iliocostalis lumborum, iliocostalis thoracis, illiacus, inferior gemellus, inferior oblique, inferior rectus, infraspinatus, interspinalis, intertransversi, lateral pterygoid, lateral rectus, latissimus dorsi, levator anguli oris, levator labii superioris, levator labii superioris alaeque nasi, levator palpebrae superioris, levator scapulae, long rotators, longissimus capitis, longissimus cervicis, longissimus thoracis, longus capitis, longus colli, lumbricals (in the hand), lumbricals (in the foot),

M – R
masseter, medial pterygoid, medial rectus, middle scalene, multifidus, mylohyoid, obliquus capitis inferior, obliquus capitis superior, obturator externus, obturator internus, occipitalis, omohyoid, opponens digiti minimi, opponens pollicis, orbicularis oculi, orbicularis oris, palmar interossei, palmaris brevis, palmaris longus, pectineus, pectoralis major, pectoralis minor, peroneus brevis, peroneus longus, peroneus tertius, piriformis, plantar interossei, plantaris, platysma, popliteus, posterior scalene, pronator quadratus, pronator teres, psoas major, quadratus femoris, quadratus plantae, rectus capitis anterior, rectus capitis lateralis, rectus capitis posterior major, rectus capitis posterior minor, rectus femoris, rhomboid major, rhomboid minor, risorius,

S – Z
sartorius, scalenus minimus, semimembranosus, semispinalis capitis, semispinalis cervicis, semispinalis thoracis, semitendinosus, serratus anterior, short rotators, soleus, spinalis capitis, spinalis cervicis, spinalis thoracis, splenius capitis, splenius cervicis, sternocleidomastoid, sternohyoid, sternothyroid, stylohyoid, subclavius, subscapularis, superior gemellus, superior oblique, superior rectus, supinator, supraspinatus, temporalis, tensor fascia lata, teres major, teres minor, thoracis, thyrohyoid, tibialis anterior, tibialis posterior, trapezius, triceps brachii, vastus intermedius, vastus lateralis, vastus medialis, zygomaticus major, zygomaticus minor.


An abnormality in the development of cartilage results in dwarfism. In some cases it is familial but in some it may be due to chromosome abnormalities. In person suffering from achondroplasia menta, sexual and reproductive development is normal.

Osteoporosis is a condition characterized by the loss of the normal density of bone, resulting in fragile bone. Osteoporosis leads to literally abnormally porous bone that is more compressible like a sponge, than dense like a brick. This disorder of the skeleton weakens the bone causing an increase in the risk for breaking bones (bone fracture).

A disease characterized by a gradual softening and bending of the bones with varying severity of pain; softening occurs because the bones contain osteoid tissue that has failed to calcify because of lack of vitamin D or renal tubular dysfunction; more common in women than in men, osteomalacia often begins during pregnancy.

A disease due to vitamin D deficiency and characterized by overproduction and deficient calcification of osteoid tissue, with associated skeletal deformities, disturbances in growth, hypocalcemia, and sometimes tetany; usually accompanied by irritability, listlessness, and generalized muscular weakness; fractures are frequent

Break in the previously normal bone (primary fracture) or previously disease bone (secondary fracture).

Fractures are classified as Simple fractures and compound fractures.

Simple Fractures: In these fractures the bone is not exposed to the external environment.
Compound fractures: In these fractures the bone is exposed to the external environment.
Management of fractures: Treatment of fractures depends on various factors like:

  1. Whether the fracture is simple or compound
  2. Whether there is any displacement of the fractured segment
  3. Age of the patient etc.

Possible methods of fracture treatment are

  1. Immobilization with external splint without reduction.
  2. Closed reduction by manipulation.
  3. Closed reduction by traction followed by immobilization with external splint or fraction.
  4. Open reduction and internal fixation.
  5. Excision of fractures segment and prosthetic replacement.

Osteomyelitis is an infection of bone and bone marrow, usually caused by pyogenic bacteria or mycobacteria. It can be usefully subclassified on the basis of the causative organism, the route, duration and anatomic location of the infection.
Types of Osteomyelitis:

  1. Pyogenic osteomyelitis (caused by staphylococcus aureus).
  2. Tuberculous osteomyelitis.
  3. Syphilitic osteomyelitis.

Treatment includes broad spectrum antibiotics and rest; sometimes surgery may be required to drain the pus.

Osteogenic sarcoma:
Malignant tumor of the bone in which the malignant cells directly form bone tissue. Genetic, constitutional and environmental influences may be predisposing factors.
These tumors usually arise at the ends of long bones (distal/proximal femur and proximal humerus). They spread (metastasize) via the blood steam, more commonly to the lungs.
Clinical features include local pain, tenderness and swelling. Treatment includes surgery.

Ewing’s Sarcoma:
This malignant tumor usually arises in children between the ages of 5 and 15. It usually develops in the shaft of the bone. Clinical features include painful enlarging mass, often tender, warm and swollen. With combined radiation, chemotherapy, and surgery there are 75 percent chances of survival.

Osteoarthritis (OA):
Osteoarthritis is a type of arthritis that is caused by the breakdown and eventual loss of the cartilage of one or more joints. Cartilage is a protein substance that serves as a “cushion” between the bones of the joints. Osteoarthritis is also known as degenerative arthritis. Among the over 100 different types of arthritis conditions, osteoarthritis is the most common, affecting over 20 million people in the United States.

Treatment includes NSAIDs and steroids.

Rheumatoid arthritis:
Rheumatoid arthritis (RA) is traditionally considered a chronic, inflammatory autoimmune disorder that causes the immune system to attack the joints. It is a disabling and painful inflammatory condition, which can lead to substantial loss of mobility due to pain and joint destruction. RA is a systemic disease, often affecting extra-articular tissues throughout the body including the skin, blood vessels, heart, lungs, and muscles.

Ankylosing spondylitis:
Chronic inflammatory joint disease of vertebrae and sacroiliac joints that usually occurs in males. Cause is supposed to be of autoimmune in origin. Symptoms are low backache, stiffness of movements of back. At later stages all the joints may be involved. Treatment includes steroid and analgesics.

Gouty arthritis: 
Inflammation of joints due to excessive production of uric acid (is the end product of nucleic acid metabolism) in the body.
Uric acid, which is in excess in the body, accumulates in the joints evoking in inflammatory response which destroys the articular cartilage and synovial membrane, the chief joint affected in big toe.
Clinical features during an acute attack include joint pain, fever and malaise.

The fluid filled synovial cavities enclosed by capsule is called Bursa.
Inflammation of the bursa is called bursitis.  The most common bursae involved are subdeltoid bursa, olecranon bursa and prepatellar bursa.

Small multiloculated cystic lesion found in the connective tissues of joint capsule or tendon sheaths. Treatment is aspiration of the fluid or removal of the cyst.

Carpel tunnel syndrome: 
Carpal tunnel syndrome (CTS) or Median Neuropathy at the Wrist is a medical condition in which the median nerve is compressed at the wrist, leading to pain, paresthesias, and muscle weakness in the forearm and hand. A form of compressive neuropathy, CTS is more common in women than it is in men, and, though it can occur at any age, has a peak incidence around age 42. The lifetime risk for CTS is around 10% of the adult population.
Most cases of CTS are idiopathic – without known cause. Repetitive activities are often blamed for the development of CTS, along with several other possible causes. However, the correlation is often unclear. 

Systemic lupus erythematosus:
Systemic lupus erythematosus (SLE or lupus) is a chronic autoimmune disease that can be fatal, though with recent medical advances, fatalities are becoming increasingly rare. As with other autoimmune diseases, the immune system attacks the body’s cells and tissue, resulting in inflammation and tissue damage. SLE can affect any part of the body, but most often harms the heart, joints, skin, lungs, blood vessels, liver, kidneys and nervous system. The course of the disease is unpredictable, with periods of illness (called flares) alternating with remission. Lupus can occur at any age, and is most common in women, particularly of non-European descent. Lupus is treatable symptomatically, mainly with corticosteroids and immunosuppressants, though there is currently no cure. However, many people with Lupus lead long and substantial lives.

Aspirin, Salicylamide, Benorylate, Diflunisal
Phenylbutazone, Oxyphenbutazone
Indomet hacin, sulindac
Ibuprofen, Naproxen, Ketoprofen, Fenoprofen, Flurbiprofen,
Diclofenac, Tolimetin
Piroxicam, Tenoxicam
Paracetamol (Acetaminophen)
Metamizol (Dippyrone), Propiphenazone

Gold, d-Penicillamime, Levamisole
Chloroquine or Hydroxychlorquine
Sulfasalazine corticosteroids


ANA          : Antinuclear antibody
C1-C7        : Cervical vertebrae
Ca             : Calcium
CPK           : Creatine phosphokinase
CTS           : Carpal tunnel syndrome
DTR           : Deep tendon reflexes
EMG          : Electromyography
ESR           : Erythrocyte sedimentation rate
IM             : Intramuscular
L1-L5         : Lumbar vertebrae
LE Cell       : Lupus erythematosus cell
Ortho        : Orthopedics,
P              : Phosphorus
RA            : Rheumatoid arthritis
RF             : Rheumatoid factor
ROM          : Range of motion
SLE           : Systemic lupus erythematosus
T1-T12       : Thoracic vertebrae
TMJ           : Temporomandibular joint