Chapter 8- Skeletal System

Midclavicular Line

(Right and left)—imaginary lines drawn vertically from the midpoints of the clavicles (collarbones) and parallel to the midsternal line.

Hyoid Bone

A U-shaped bone located in the upper neck. It anchors the tongue and is associated with swallowing. The hyoid bone is often fractured during strangulation.

Ball-&-Socket Joint

A ball-and-socket joint is formed when the ball-shaped end of one bone fits into the cup-shaped socket of another bone, allowing the bones to move in many directions around a central point. The shoulder and hip joints are ball-and-socket joints. The head of the humerus fits into the glenoid cavity of the scapula in the shoulder joint. The head of the femur fits into the acetabulum of the coxal bone in the hip joint.

Rheumatology

A branch of medicine that studies disease of the joints.

Arthrology

A branch of science that studies joints.

Symphysis Pubis

A cartilaginous joint that is the point of fusion for two pubic bones. A disc of cartilage separates the pubic bones at the symphysis pubis.

Sinus

A cavity or hollow space.

Condyloid Joint

A condyloid joint is formed when the oval articular surface of one bone fits into the oval depression of the second articulating bone. The radiocarpal joint (wrist) and the metacarpophalangeal joints (knuckles) at the bases of the fingers are examples of condyloid joints.

Olecranon

A depression of the humerus that holds the olecranon process of the ulna when the elbow is extended (not bent).

Fossa

A depression or groove.

Gliding Joint

A gliding joint is formed by the interaction of the flat surfaces of the articulating bones. A gliding joint allows for a limited but complex gliding movement. Gliding joints are found in the wrist (intercarpal joints), ankle (intertarsal joints), and vertebral column.

Epiphyseal Disc

A growing long bone contains a band of hyaline cartilage located near the proximal and distal ends of long bones. This band of cartilage is the epiphyseal disc, or growth plate. It is here that longitudinal bone growth occurs.

Angle of Louis (sternomanubrial joint)

A joint that is referenced in counting ribs. The joint is located at the level of the second rib.

Joints (Articulations)

A joint, or articulation, is the site where two bones meet. Joints perform two functions: they hold the bones together, and they provide flexibility to a rigid skeleton. Joints can be classified into three groups according to the amount of movement: immovable, slightly movable, and freely movable. Joints can also be classified according to the types of tissues—fibrous, cartilaginous, or synovial—that bind the bones at the joint.

Tubercle

A knoblike projection.

Obturator Foramen

A large hole is formed as the pubic bone fuses with a part of the ischium. The obturator is the largest foramen in the body.

Condyle

A large rounded knob that usually articulates with another bone.

Trochanter

A large tubercle (tuberosity) found only on the femur.

Fibula

A long, thin bone positioned laterally alongside the tibia in the leg. The proximal end of the fibula articulates with the tibia. It does not articulate with the femur, is not part of the knee, & bears much less weight than does the tibia. The distal end forms the lateral malleolus, which articulates with the talus. The articulation of the distal tibia (medial malleolus) & fibula (lateral malleolus) with the talus forms the ankle joint or talocrural joint.

Pivot Joint

A pivot joint allows for rotation around the length of a bone. The pivot joint allows only for rotation. An example is the side-to-side movement of the head indicating "no." This rotation occurs as the atlas (first cervical vertebra) swivels around, or pivots, on the axis (second cervical vertebra). This joint is called the atlantoaxial joint.

Process

A prominent projection on a bone.

Tibial Tuberosity

A protuberance is the site of attachment for the muscles and ligaments from the thigh.

Crest

A ridge on bone.

Saddle Joint

A saddle joint is formed when the surfaces of both articulating bones are saddle-shaped; the saddle shape of one bone is concave whereas the saddle shape of the second bone is convex. The position of the articulating bones is like a rider in a saddle.

Spine

A sharp projection.

Facet

A small flattened surface.

Laminectomy

A surgical procedure that may be performed to access the intervertebral disc; the opening allows the surgeon to remove a damaged, or "slipped," disc.

Spinal Fusion

A technique to immobilize part of the spine by joining together (fusing) two or more vertebrae.

Thoracic Cage

A term that refers to the chest region. The thoracic cage is the skeletal part of the chest; it is a bony, cone-shaped cage that surrounds & protects the lungs, heart, large blood vessels, & some of the abdominal organs, such as the liver, spleen, & kidneys. The thoracic cage plays a crucial role in breathing.

Periosteum

A tough, fibrous, connective tissue membrane that covers the outside of the diaphysis. It is anchored firmly to the outside of the bone on all surfaces except the articular cartilage. The periosteum protects the bone, serves as a point of attachment for muscle, and contains the blood vessels that nourish the underlying bone. Because the periosteum carries the blood supply to the underlying bone, injury to this structure has serious consequences to the health of the bone. Like any other organ, the loss of blood supply can cause its death.

Meatus

A tunnel or tubelike passageway.

Sinuses

Air-filled cavities located in several of the bones of the skull. They perform two important functions. They lessen the weight of the skull, and they modulate the sound of the voice. The four sinuses are called the paranasal sinuses because they surround and connect with the nasal structures. The names of the four sinuses reflect their location within the various skull bones: frontal sinus, ethmoidal sinuses, sphenoidal sinus, and maxillary sinuses.

Vertebral Column

Also called the backbone or spine, extends from the skull to the pelvis. The vertebral column consists of 26 bones, called vertebrae, aligned & stacked in a column. Sitting between each vertebra is a cartilaginous disc. The vertebrae are named according to their location. Seven cervical vertebrae (C1 to C7) are located in the neck region.

Hip

Also called the coxal joint, is a ball-and-socket joint formed where the head of the femur articulates with the acetabulum, the depression formed by the three coxal bones. The hip is strengthened by surrounding muscles, tendons, and ligaments. A fractured hip refers to a break in the neck of the femur.

Shoulder

Also called the glenohumeral joint, indicates that the head of the humerus fits into the glenoid cavity of the scapula. The shoulder joint is a ball-&-socket joint that permits the greatest range of motion. The joint is stabilized by surrounding skeletal muscles, tendons, & ligaments. The rotator cuff muscles and tendons, in particular, hold the head of the humerus in the glenoid cavity.

Elbow

Also called the humeroulnar joint. A lesser component of the elbow is the humeroradial joint. The olecranon process of the ulna forms the pointy part of the elbow when it is flexed. The elbow is a hinge joint that is very stable; nonetheless, it can be injured.

Knee

Also called the tibiofemoral joint, is a hinge joint. In addition to all the structures contained in a synovial joint, the knee joint contains extra cushioning in the form of pads of cartilage. These pads absorb the shock of walking and jumping. Two crescent-shaped pads of cartilage, the medial meniscus & lateral meniscus, rest on the tibia. Like other synovial joints, the knee joint is reinforced and aligned by supporting ligaments, the cruciate ligaments in particular. There is an anterior cruciate ligament (ACL) and a posterior cruciate ligament (PCL).

Sternum

Also known as the breastbone, is a dagger-shaped bone located along the midline of the anterior chest. The three parts are the manubrium, body, & xiphoid process. The xiphoid process is the tip of the sternum & serves as a point of attachment for some abdominal muscles. Note the suprasternal notch (also called the jugular notch), a depression on the upper part of the manubrium between the two clavicles; it is used as a landmark to locate other structures.

Head

An enlarged and rounded end of a bone.

Epicondyle

An enlargement near or above a condyle.

Midsternal Line

An imaginary line drawn vertically from the suprasternal notch through the middle of the sternum.

Sinusitis

An inflammation of the sinus.

Foramen

An opening through a bone; usually serves as a passageway for nerves, blood vessels, and ligaments.

Osetoblasts

Bone cells that secrete an intercellular matrix, containing calcium, other minerals, & protein fibers. The osteoblasts mature into osteocytes that sit within the hard bone matrix & maintain the bone.

Osseous Tissue

Bone tissue.

Foot

Each foot has an ankle, instep, & five toes. Seven tarsal bones form the ankle. The most proximal of the tarsal bones, the talus, articulates with the tibia and fibula. Most of the weight of the body is supported by two of the tarsal bones, the talus & the calcaneus or heel bone. The instep of the foot is formed by five metatarsal bones. The ball of the foot is formed by the distal ends of the metatarsals. The tarsals, metatarsals, & associated tendons and ligaments form the arch of the foot.

Trochanters

Large and small processes for tendon attachments. These trochanters provide sites of attachment for many muscles.

Long Bones

Long bones are longer than they are wide. They are found in the arms, forearms, palms, fingers, thighs, legs, and instep. Although it is obvious that the femur (thigh) & the humerus (arm) are long bones, even small bones such as the metacarpals & finger bones are considered long bones.

Fontanels

Meaning "little fountains." The rhythm of the baby's pulse can be felt in these soft spots. The two major fontanels are the larger, diamond-shaped anterior fontanel and the smaller, posterior occipital fontanel. Two smaller fontanels are located more laterally—the anterolateral and posterolateral fontanels. By the time a child reaches 2 years of age, these fontanels have been gradually converted to bone and can no longer be felt.

Hydrocephalus

Means "water on the brain."

Endosteum

Membranous lining of the hollow cavity of the bone.

Moving Synovial Joints

The body contains many types of freely movable synovial joints. The type of motion & the degree of flexibility vary with each type of joint. For example, if you move your elbow, your forearm will move like two boards joined by a hinge. This motion is very different from the arm-swinging motion at the shoulder joint. Both the elbow & shoulder joints are freely movable, but the types of movement differ.

Ribs

The bones in the chest that protect the heart and lungs. Note that the ribs are numbered, which allows us to describe the location of thoracic structures. The spaces between the ribs (intercostal spaces) are also numbered.

Floating Ribs

The bottom two pairs of false ribs lack sternal attachment.

Clavicle

The clavicle is also called the collarbone. It looks like a long, slender, S-shaped rod & articulates with both the sternum & scapula. The clavicle helps stabilize the shoulder; the attachment, however, is weak. The clavicle is easily dislocated & is the most frequently broken bone in the body.

Coxal Bone

The coxal bone is the hip bone. Each coxal bone is composed of three parts: the ilium, ischium, & pubis.

Cranium

The cranium is a bony structure that encases and protects the brain. The cranium is composed of eight bones, most of which are curved and flat.

Costal Margins

The edges of the cartilage that form an angle as they converge near the xiphoid process.

Epiphysis

The enlarged ends of the long bone. The epiphysis of a bone articulates, or meets, with a second bone at a joint. Each epiphysis consists of a thin layer of compact bone overlying spongy bone. The epiphyses are covered by cartilage.

Pollex

Pertaining to the thumb which only has two bones.

Other Facial Bones

Several other bones complete the facial structure, including the lacrimal bones, nasal bones, vomer, and inferior nasal conchae.

Short Bones

Short bones are shaped like cubes and are found primarily in the wrists and ankles.

Slightly Moveable Joints

Slightly movable joints permit limited movement. Limited movement is usually achieved by bones connected by a cartilaginous disc.

Spongy Bone

Spongy, or cancellous, bone is less dense. Spongy bone is located primarily at the ends of long bones & in the center of other bones.

Trabeculae

Supporting bundles of bony fibers in cancellous (spongy) bone.

Phalanges

The 14 finger bones that are also known as digits.

Sacrum

The ancients thought that the seat of the soul was located at the base of the spine & therefore called the sacred area the "sacrum."

Costal Angle

The angle formed by the intersection of the costal margins; it should be less than 90 degrees. The costal angle can change size.

Appendicular Skeleton

The appendicular skeleton is composed of the bones of the shoulder girdle, upper limbs, pelvic girdle, & lower limbs.

Articular Cartilage

The articular cartilage is found on the outer surface of the epiphysis. It forms a smooth, shiny surface that decreases friction within a joint. Because a joint is also called an articulation, this cartilage is called articular cartilage.

Ethmoid Bone

The ethmoid bone is an irregularly shaped bone located between the eye orbits; it is the major supporting bony structure of the nasal cavity. A projection of the ethmoid bone forms a point of attachment for the meninges, the membranes that surround the brain and contain cerebrospinal fluid. The location and shape of the ethmoid bone have important clinical implications.

Facial Bones

The face has 14 facial bones, most of which are paired. Only the mandible and the vomer are single bones.

Femur

The femur is the thigh bone; it is the longest & strongest bone in the body. The femur articulates proximally with the coxal bone to form the hip joint & distally with the bones of the leg to form the knee joint. The head of the femur sits in the acetabulum of the coxal bone and allows the thigh to rotate at the hip joint. The head of the femur attaches to the rest of the femur by the neck. A number of bony processes are on the femur.

Atlas

The first cervical vertebra (C1) is called the atlas. The atlas has no body but does have depressions into which fit the bony projections of the occipital bone of the skull. The atlas supports the skull and allows you to nod "yes." The atlas is named after a figure in Greek mythology, Atlas, who carried the earth on his shoulders.

Frontal Bone

The frontal bone forms the forehead and the upper part of the bony structure surrounding the eyes.

Hand

The hand is composed of a wrist, palm, and fingers. The wrist contains eight bones called carpal bones, which are tightly bound by ligaments. Five metacarpal bones form the palm of the hand; each metacarpal bone is in line with a finger.

Hinge Joint

The hinge joint allows movement similar to the movement of two boards joined together by a hinge. The hinge allows movement in one direction, where the angle at the hinge increases or decreases. Hinge joints include elbows, knees, and fingers.

Humerus

The humerus is the arm bone. The proximal humerus contains a head, which fits into the glenoid cavity of the scapula, allowing the arm to rotate at the shoulder joint. At the distal end of the humerus are several processes that allow it to articulate with the bones of the forearm.

Infant Skull

The infant skull has areas that have not yet been converted to bone. Instead, they are covered by a fibrous membrane. Because these areas are soft to touch, they are called a baby's soft spots.

Illium

The largest part of the coxal bone. The ilium is the flared upper part of the bone & can be felt at the hip. The ilium connects in the back with the sacrum, forming the sacroiliac joint. The greater sciatic notch is the site where blood vessels and the sciatic nerve pass from the pelvic cavity into the posterior thigh region. Like the sternum, the ilium produces blood cells and is a site for bone marrow biopsy.

Diaphysis

The long shaft of the bone. It is composed primarily of compact bone and therefore provides considerable strength.

Mandible

The lower jaw bone, carries the lower teeth. The anterior portion of the mandible forms the chin. The mandible forms the only freely movable joint in the skull. Two posterior upright projections on the mandible have bony processes that articulate with the temporal bones at the temporomandibular joint (TMJ). The TMJ can be felt as the depression immediately in front of the ear. Tension or stress often causes pain in the TMJ. This condition is often associated with tooth grinding (bruxism) during sleep. Bony processes on the mandible serve as points of attachment for chewing muscles.

Lower Limbs

The lower limb includes the bones of the thigh, kneecap, leg, and foot.

Medullary Cavity

The medullary cavity is the hollow center of the diaphysis. In infancy, the cavity is filled with red bone marrow for blood cell production. In the adult, the medullary cavity is filled with yellow bone marrow and functions as a storage site for fat. The inside of the medullary cavity is lined with connective tissue called the endosteum.

Osteon

The microscopic unit of compact bone. It is also known as the haversian system. Each haversian system consists of mature osteocytes arranged in concentric circles around large blood vessels.

Pubis

The most anterior part of the coxal bone.

Ischium

The most inferior part of the coxal bone. The ischium contains three important structures: the ischial tuberosity, the ischial spine, & the lesser sciatic notch. The ischial tuberosity is the part of the coxal bone on which you sit. The ischial spine projects into the pelvic cavity and narrows the outlet of the pelvis.

Occipital Bone

The occipital bone is located at the back and base of the cranium. The large hole in the occipital bone is called the foramen magnum. The foramen allows the brain stem to extend downward and become the spinal cord. On either side of the foramen magnum are bony projections, called occipital condyles that sit on the first vertebra of the vertebral column.

Vertebral Foramen

The opening for the spinal cord; the vertebral foramen of the stacked vertebrae form the vertebral canal. The vertebrae are aligned so that if you run your hand down your back, you will feel the spinous processes. For this reason, the vertebral column is also called the spine.

Iliac Crest

The outer edge of the ilium.

Patella

The patella is the kneecap. It is a triangular bone located within a tendon that passes over the knee. It articulates with both the distal femur and protects the anterior surface of the knee joint.

Pelivc Girdle

The pelvic girdle is composed of two coxal bones that articulate with each other anteriorly and with the sacrum posteriorly (Fig. 8.15A). The pelvic girdle performs three functions. 1. It bears the weight of the body. 2. It serves as a place of attachment for the thighs 3. It protects the organs located in the pelvic cavity, including the urinary bladder and reproductive organs.

Pelvis

The pelvis is formed by the pelvic girdle, sacrum, & coccyx.

Ossification

The process of bone formation. Ossification begins in the late embryonic period with the formation of fibrous connective tissue and hyaline cartilage that is shaped like a mini skeleton. As the fetus matures, the cartilage and connective tissue change into bone. Ossification occurs in two ways. Intramembranous ossification & endochondral ossification.

Bone Surface Markings

The projecting bone markings (the markings that stick out) serve as points of attachment for muscles, tendons, and ligaments. The grooves and depressions form the routes traveled by blood vessels and nerves as they pass over and through the bones and joints. The projections and depressions also help form joints.

Radius

The radius is one of two bones of the forearm. It is located on the lateral or thumb side when the palm of the hand is facing forward. The head of the radius articulates with the humerus and proximal ulna, whereas the distal end articulates with the distal ulna and the carpal or wrist bones. The radial tuberosity at the proximal end of the radius is the site of attachment for one of the muscles responsible for bending the forearm at the elbow.

Scapula

The scapula also called the shoulder blade or wing bone is a large flat bone shaped like a triangle. The two scapulae are located on the posterior thorax. Two large processes on the scapula allow it to articulate with the clavicle and serve as points of attachment for arm & chest muscles. The glenoid cavity on the scapula is the site where the head of the humerus (arm bone) fits, thereby allowing you to rotate your arm at the shoulder.

Axis

The second cervical vertebra (C2) is called the axis. The axis has a projection, called the dens (nicknamed for the toothlike odontoid process), which fits into the atlas and acts as a pivot or swivel for the atlas. The axis allows your head to rotate from side to side as you say "no."

Tibia

The shinbone and articulates with the distal femur at the knee. The tibia is the larger weight-bearing bone of the leg.

Shoulder Girdle

The shoulder girdle is also called the pectoral girdle. Each shoulder girdle contains two bones: one clavicle & one scapula. The shoulder girdle supports the upper limbs & serves as a place of attachment for muscles. The shoulder girdle is designed for great flexibility

The Skeletal System

The skeletal system consists of the bones, joints, & cartilage & ligaments associated with the joints. Bone tissue is living & metabolically active, but because it contains so much nonliving material, such as calcium & phosphorus, it appears dead or dried up. In fact, the word skeleton comes from a Greek word meaning "dried-up body." The skeletal system, however, is anything but dead. It contains 206 bones that are very much alive & perform a number of important functions.

Skull

The skull sits on top of the vertebral column and is formed by two groups of bones: the cranium and the facial bones.

Sphenoid Bone

The sphenoid bone is a butterfly-shaped bone that forms part of the floor and sides of the cranium. The sphenoid bone also helps form the orbits surrounding the eyes. In the midline of the sphenoid bone is a depression called the sella turcica (Turk's saddle); it forms the seat for the pituitary gland.

Sutures

The sutures join together the bones of the skull, much like a zipper. The major sutures include the coronal suture, the lambdoidal suture, and the squamosal suture. Unlike other joints in the body, no significant movement occurs between cranial bones.

Microcephalia

The sutures of the infant skull fuse too early, preventing the growth of the brain. It is characterized by a small cranium, restricted brain growth, & impaired intellectual functioning. Sometimes the skull expands too much.

Coccyx

The tailbone is called the coccyx because it resembles the beak of a cuckoo bird.

Parietal Bone

The two parietal bones form the upper sides of the head and the roof of the cranial cavity (top of the head).

Temporal Bones

The two temporal bones are on the sides of the head, close to the ears (commonly called the temples). Several important bone markings are found on the temporal bones. - External auditory meatus: An opening for the ear - Zygomatic process: Articulates with the cheekbone - Styloid process: A sharp projection used as a point of attachment for several muscles associated with the tongue and larynx. - Mastoid process, which forms a point of attachment for some of the muscles of the neck. Here's an interesting note about the temporal bone. Tempor is a Latin word meaning "time." As men age, over time, they usually develop their first gray hairs over the temple area. So, the name of the temporal bone is a reference to aging.

Ulna

The ulna is the second bone of the forearm. The longer of the two bones, the ulna, is located on the medial or little finger side of the forearm. It has processes & depressions that allow it to articulate with the humerus & radius proximally and with the radius distally.

Upper Limbs

The upper limbs contain the bones of the arm (humerus), forearm (ulna and radius), & hand (carpals, metacarpals, & phalanges).

Vertebra

The vertebra is an irregular bone that contains several distinct structures. The body of the vertebra is padded by a cartilaginous disc & supports the weight of the vertebra sitting on top of it. Some processes provide sites of attachment for ligaments, tendons, and muscles; other processes articulate with bones such as the ribs.

Zygomatic Bones

The zygomatic bones are the cheekbones. They also form a part of the orbits of the eyes.

Circumduction

This is a combination of movements, as in the circular arm movement that a softball pitcher makes while pitching the ball.

Plantar Flexion

This is bending the foot down, as in toe dancing.

Dorsiflexion

This is bending the foot up toward the leg.

Abduction

This is movement away from the midline of the body (move your leg sideways, away from your body).

Adduction

This is movement toward the midline of the body (return your leg toward your body).

Hyperextension

This is overextending the joint beyond its normally straightened position, as in moving the hand toward the upper surface of the wrist.

Flexion

This is the bending of a joint that decreases the angle between the bones (bending the leg at the knee or the fingers).

Extension

This is the straightening of a joint so that the angle between the bones increases (e.g., straightening the leg at the knee or the fingers to open the hand).

Pronation

This is turning the hand so that the palm faces downward.

Supination

This is turning the hand so that the palm faces upward.

Inversion

This is turning the sole of the foot inward so that it faces the opposite foot.

Eversion

This is turning the sole of the foot outward.

Ossicles

Three tiny bones in the middle ear.

T1 to T12

Twelve thoracic vertebrae (T1 to T12) are located in the chest region.

Maxilla

Two maxillary bones fuse to form the upper jaw. The maxilla carries the upper teeth. An extension of the maxilla, the palatine process, forms the anterior portion of the hard palate (roof) of the mouth. These bones also form parts of the nasal cavity and the eye orbits.

Palatine Bones

Two palatine bones form the posterior part of the hard palate and the floor of the nasal cavity. Failure of the palatine and/or maxillary bones to fuse causes a cleft palate (an opening in the roof of the mouth), making suckling very difficult for an infant and contributing to a host of other developmental issues. Fortunately, a cleft palate can be surgically repaired.

Acetabulum

When the three coxal bones join together to form a depression. The acetabulum is important because it receives the head of the femur and therefore enables the thigh to rotate at the hip joint.

Curvatures

When viewed from the side, the vertebral column has four normal curvatures. The cervical, thoracic, lumbar, and sacral curves. The directions of the curvatures are important. The cervical and the lumbar curvatures bend toward the front of the body. The thoracic and sacral curvatures bend away from the front of the body. These curves center the head over the body, thereby providing the balance needed to walk in an upright position.

Immoveable Joints

Immovable joints permit no movement. The sutures in the skull are immovable joints. The sutures are formed as the irregular edges of the skull bones interlock and are bound by fibrous connective tissue. When fused, they look like zippers.

Axial Skeleton

Includes the bones of the cranium, face, middle ear bones, hyoid bone, vertebral column, & bony thorax.

Appendicular Skeleton

Includes the bones of the pelvic girdle, the upper extremities (arms, forearms, wrist, palms, and fingers), & lower extremities (thighs, legs, ankles, instep, and toes).

Irregular Bones

Irregular bones are differently shaped and are not classified as long, short, or flat. They include the hip bones, vertebrae, and various bones in the skull.

Vertebra Prominens

It is used as a landmark in assessing surface anatomy. The large vertebra is C7.

True Ribs

Anteriorly, the top seven pairs of ribs attach directly to the sternum by costal cartilage.

Medial Mallelous

At the distal end of the tibia, a protuberance articulates with the talus, a tarsal bone.

Compact Bone

Dense, hard bone tissue found primarily in the shafts of long bones and on the outer surfaces of other bones.

L1 to L5

Five lumbar vertebrae (L1 to L5) are located in the lower back region.

False Ribs

Five pairs attach indirectly to the sternum by cartilage or do not attach at all.

Flat Bones

Flat bones are thin, flat, and curved. They form the ribs, breastbone, cranium, and bones of the shoulder girdle.

Freely Moveable Joints

Freely movable joints provide much more flexibility and movement than the other two types of joints. Most of the joints of the skeletal system are freely movable. All freely movable joints are known as synovial joints.