Skeletal System in Man

SKELETAL SYSTEM IN MAN
Human skeleton is made of 206 bones which have formed from some 300 bones through
fusion. The bones are arranged into axial and appendicular skeleton. Number of bones in
child = 350
Axial Skeleton
It is part of endoskeleton which occurs along the middle longitudinal axis of the body. Axial
skeleton has 80 bones forming four structures — skull, vertebral column, sternum and ribs.
Skull (29 bones)
It constitutes skeleton of the head region. Skull consists of four parts — cranium, facial
bones, hyoid and ear bones.
Fig. Skull of Human (lateral view)

Cranium (Brain Box, 8 bones). It is the bony structure which encloses the brain and protects
it. It is hollow and nearly rounded. Bones constituting the cranium are called
cranial bones. They are eight in number.
(i) Frontal-1 (ii) Parietal-2 (iii) Occipital-1 (iv) Temporal-2 (v) Sphenoid-1 (vi) Ethmoid- 1.
1. Cranial bones are flattened bones. They are jointed with one another by fixed
interdigited joints called sutures.
2. At the base of skull occipital has a very large opening called foramen
of magnum (largest foramen). Through foramen of magnum brain communicates with
spinal cord.
3. There are two lateral protuberances or occipital condyles, one on each side of
foramen magnum.
4. Because of the presence of two occipital condyles, human skull is called dicondylic.
5. The two occiptial condyles are articulated with atlas vertebra by hinge joints
for performing nodding movements.
 Ear Ossicles (6 bones).
1. Each side or temporal region contains an auditory capsule or middle ear.
2. It has three bones. These bones are small in size and named as ear ossicles or
ear bones. They are outer malleus (hammer shaped), middle incus (anvil shaped) and
innermost stapes (stirrup shaped).
3. These bones are helpful in the amplification of sound by 20-22 times
 Facial Bones (14 bones).
1. Facial bones constitute front part of skull along with skeleton of lower jaw, hard
palate and nose. They are fourteen in number.
Nasals-2 (ii) Maxillae-2 (iii) Zygomatic (cheek bones)-2 (iv) Lacrimals-2 (v)
Palatines-2 (vi) Inferior nasal conchae-2 (vii) Vomer-1 (viii) Mandible-1.
2. Frontal is common bone to both cranium and face.
3. Maxillae form the upper jaw whereas mandible forms the lower jaw.
4. Upper jaw is fused with cranium.
5. Lower jaw or mandible is horse-shoe shaped bone which bears two processes on each
side, a pointed one named coronoid and a rounded one called condyloid.
6. Mandible is strongest and largest bone of face.Movable mandible helps in the
mastication of food as well as speech.
7. Jaws have sockets for the fixation of teeth.
 Hyoid Bone (Tongue Bone; 1 bone).

1. It lies at the base of tongue and above the larynx.
2. It is not joined to the rest of skeleton except to styloid process of temporal bone by
muscles with the help of certain muscles.
3. It is horse shoe-shaped slender bone. Upper portion of hyoid bone has a swelling
known as the greater cornu.
4. The lower portion has small projection known as lesser cornu.
5. Hyoid bone and the tongue together form the hyoid apparatus.
Fig. Human hyoid bone

Vertebrae (sing: Vertebra) are a series of bones that make up the vertebral column (or spine)
in all vertebrate species. Our vertebral column is composed of 33 irregular sized bones that
are connected to each other by intervertebral discs.
The vertebral column is divided into five regions – cervical (7), thoracic (12), lumbar (5),
sacral (1-fused) and coccygeal (1-fused).
In the adult stage of man number of vertebrae are as follows –
Cervical (in neck) 7
Thoracic (in chest or thorax) 12
Lumbar ( in loins) 5
Sacral (in upper part of pelvis) 1 (formed of five fused vertebrae)
Coccygeal or Coccyx (in lower part of
1 (formed of four fused vertebrae)
pelvis)
Cervical vertebrae:
The first seven vertebrae of the vertebral column constitute the cervical vertebrae. These are
small sized and present in the neck region. The first vertebra is called atlas and second is
called axis.
1, 2, 7 cervical vertebrae are atypical and 3, 6 are typical.
Atlas supports the head and consists of a complete ring of bone. On its upper surface, facets
for articulation with the condyles of the occipital bone, forming a condyloid joint at which the
nodding movement of head take place.
Axis is the pivot on which the atlas turns in the rotatory movements of the head. From the
body of the axis a process of bone rises which is called odontoid peg which articulates with
the back of the anterior arch of the atlas. The atlas moves round the odontoid peg of the axis,
forming a pivot joint at which the head rotates.
Atlas Axis Cervical vertebrae

First cervical vertebra. Second cervical vertebra. Long neural spine.
Body is formed by centrum Centrum acoelus. Centrum acoelus.
and vertebral arch.
Articulates with condyles of Odontoid process present. Transverse process are large.
the occipital bone
Centrum is absent. It is pivot for rotation of Vertebral canals present.
atlas and head around
odontoid process.
Neural spine reduced. Transverse process small.
Transverse process are long.
Thoracic vertebrae
Thoracic vertebrae are larger than the cervical vertebrae and are located in the chest. There
are 12 thoracic vertebrae which contains sites for the attachment for ribs. The ribs attach to
the thoracic vertebraeand protect heart and lungs.
Thoracic 2-8 are typical. 1,9,1,11,12 are typical.
Thoracic vertebra
Centrum acoelus.
Neural canal is formed by union of two neural arches.
Neural spine is a flat & long directed backward.
Club shaped transverse process.
Neural arch with superior articular process.
Two demifacets for articulation of head of a rib are present.
Lumbar vertebrae:
It is the strongest, thickest and largest vertebrae present in the vertebral column. It consist of
5 vertebrae present in the abdomen, which bear the weight of the trunk.
Lumbar vertebrae:
Centrum acoelus.
Neural spine well developed.
Transverse process are thin and long.
Small accessory process present near the root of each transverse process.
It is the largest vertebrae
Sacral vertebrae
It is fusion of five vertebrae. It fuses to form a triangular bony complex or structure called
sacrum.
It is present in the pelvic region.
Sacral canal is formed by sacral vertebral foramina.
In female sacrum is shorter and wider.
Transverse process is much modified into a broad sloping mass project laterally from the
body.
Coccyx
It is formed by fusion of four caudal vertebrae.
It is last section of backbone.
It is small triangular bone.
Two coccygeal cornua project up to articulate with sacral cornua.
Rudimentary transverse process.
. A. Typical cervical vertebra. B. Atlas and axis. C. Typical thoracic vertebra. D. Typical
lumbar vertebra. Regional vertebrae. E. Sacrum. F. Coccyx.
Girdles
They are bony supporting complexes of skeleton which mediate attachment of limb bones to
axial skeleton. There are two girdles, pectoral and pelvic.
 Pectoral Girdle (Shoulder Girdle).
1. It is supporting bony complex between upper limbs and axial skeleton.
2. Pectoral girdle consists of two halves, right and left.
3. Each half consists of two bones, clavicle and scapula.
4. Clavicle or collar bone is f-shaped twice curved, thin and elongated bone. At one end
it is connected with acromion process of scapula and at the other end it is attached to
manubrium of sternum.
5. Scapula is a flat, thin curved triangular bone, popularly called shoulder blade. It
extends on the back side of thorax between second and seventh rib. It has a hook- like
coracoid process and a diagonally placed sharp protuberance called spine. At one end
spine possesses thick acromion process.
6. Scapula contains glenoid cavity for articulation with head of humerus.
Fig. Pectoral girdle (Posterior view)

1. Pelvic Girdle
1. It is an irregular trough-shaped supporting bony complex between hind limbs and
axial skeleton.
2. Pelvic or hip girdle consists of two halves called innominates or coxals.
3. Innoniminates are joined together by little movable pubic symphysis.
4. Each innominate consists of three fused bones—largest superior ilium, anterior
inferior pubis and posterior inferior ischium.
5. A large oval gap called obturator foramen occurs between pubis and ischium.
6. Ilium, ischium and pubis jointly form an articular cavity called acetabulum. Head
of femur bone is fixed into it.
7. Pelvic girdle is attached posteriorly to sacrum. Sacrum and coccyx form basin
shaped pelvis.
8. Ilium possesses two depressions, small lesser sciatic notch and large greater
sciatic notch.
Fig. Anterior view of pelvis (hip girdle + sacrum + coccyx)
LIMB BONES
They are of two types, fore limbs and hind limbs.
Bones of Fore-Limbs.
1. There is a pair of fore-limbs or upper limbs.
2. Each fore-limb has 30 bones and three parts—upper arm, lower or fore-arm and hand.
3. Upper arm has only one bone, fore arm two bones while remaining 27 bones belong
to hand.
4. Humerus is the single long bone of upper arm. Its body is called shaft. Upper or
proximal end bears a round head. Below it is present a narrow neck and two
tuberosities— greater tuberosity and lesser tuberosity. A deltoid tuberosity occurs
over the shaft- Distal end of humerus has a pulley-like trochlea (attachment of ulna),
convex capitulum (attachment to radius) and outgrowths or epicondyles.
5. The two bones of fore or lower arm are radius and ulna. Both are curved with radius
towards thumb side and ulna towards the side of little finger. The two bones may lie
parallel to each other or cross each other.
6. The latter happens when palm is kept in backward position. Radius is shorter than
ulna. Its lower end is broader with two articular facets for carpals. Proximal end of
ulna is elongated to form olecranon that produces elbow joint. Distal end of ulna has
one facet for attachment of carpal.
Bones of Hind Limbs (Lower Extremities).

1. Bones of a hind limb are thirty in number—one in thigh, two in shank, one over knee
and 26 in the foot region.
2. The single bone of thigh is called femur. Femur is the longest bone. It has a body or
shaft. The upper end is swollen into head which fits in acetabulum of pelvic girdle.
Head is followed by a narrow neck and two ridges, greater trochanter and lesser
trochanter. Shaft is curved. Its concave side has a ridge. The distal end of femur has a
central groove and two lateral condyles. A triangular disc-shaped patella or knee cap
fits over intercondylar groove.
3. The two bones of shank are tibia and fibula. Tibia is inner and thicker with a sharp
crest. Its proximal end has concave facets for fitting over condyles of femur. Distally,
it bears a projection on inner side called medial malleolus. Fibula is outer and slender
bone of shank which is projected distally to form external malleolus.
Fig. Human Pelvic girdle, sacrum, coccyx & bones of leg

Skeletal System in Man

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SKELETAL SYSTEM IN MAN

Fig. Skull of Human (lateral view)

 Hyoid Bone (Tongue Bone; 1 bone).

Fig. Human hyoid bone

Atlas Axis Cervical vertebrae

Fig. Pectoral girdle (Posterior view)

Fig. Anterior view of pelvis (hip girdle + sacrum + coccyx)

Bones of Hind Limbs (Lower Extremities).

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