Human Skeletal System

The skeleton is the framework that allows humans to carry out all of these tasks, such as; Walking and running, as well as crawling, jumping, and climbing. At birth, humans have up to 300 bones. With age, however, the bones begin to merge. The total number of bones in an adult’s body is decreased to 206.

The heart, lungs, and liver are among the important organs that the skeleton protects. Ligaments, a fibrous connective tissue, connect bones to one another.

The locations where two or more bones connect are called joints. Joints are divided into moveable and immovable joints based on their flexibility and movement. Immovable joints (also known as fixed joints) are non-flexible, whereas moveable joints are flexible.

Also read: Weight of Human Organ

The skeletal structure of a body is embraced of bones, tendons, ligaments, and cartilages. The chief utility of the skeletal structure is to provide support and movement to the body. Besides this, the skeletal system protects the inner structures and delicate body organs like the heart, brain, kidney, lungs, etc. The cranium protects the brain and eyes, while the ribs defend the heart and lungs. Similarly, the vertebra protects the spinal cord. The bones are held with the help of tendons which are hard inflexible bands. A usual bone has an external coating of the firm or compacted bone that is extremely durable, thick, and hard, and below it, there is a specific coating of spongy bone, that looks like a honeycomb, lighter, and a little stretchy. The central of certain bones have jelly-like bone marrow, in which new cells are continuously formed for the blood.

Types of Bones

Bones can be characterized rendering to their general form:

Long Bones

The long bones are found in the limbs, and each consists of a body or shaft and two extremities. As the term specifies, these bones are long in size, cylindrical, and have wide rigid levers for muscle actions. The elongated bones are not right-angled, but bent, the bend usually takes place in double planes, thus giving larger strength to the bone. The bones included in this category are the clavicle, humerus, radius, ulna, femur, tibia, and fibula.

Long Bones of Upper Extremity


The Humerus is the elongated and biggest bone of the upper extremity i.e. upper arm bone. It is separated into a body and two extremes. It is a cylindrical shaft-like bone that has a flattened distal end and a rounded articular surface at the proximal end. The higher termination of the humerus contains the head, which projects into the glenoid cavity.


The radius is the lateral bone of the forearm. It is located on the adjacent side of the ulna and sideways forms the skeletons of the forearm. These bones are coherent with the humerus at the proximal termination and the wrist bones at the distal end.


It is the intermediate bone in the forearm which is corresponding to the radius. At the proximal end, it has a hook-like articular exterior. The distal end comprises a rounded head and a styloid process.

Long Bones of Lower Extremity


It is the human body’s longest and strongest bone. It is practically cylindrical in the superior part. In the straight position, it is not upright, has a separate head-like structure at the upper end, and is associated with a significant intermission that relates to the extent of the pelvis. It again inclines in progressively descending manner medial wards in the direction of its inferior part, to form the knee joint. The extent of this leaning differs in various individuals, and is superior in the woman than in the man, on the expansion of the superior extent of the pelvis.


It is present in the central position of the leg having prismoid arrangement with prolonged overhead, where it forms the knee-joint, constricted in the inferior third, and over enlarged but to a lesser extent at the lower end. It has a body and two extremes. In the male, its track is perpendicular and corresponds with the bone of the contrasting side. On the other hand in the female, it consists of descending diagonal track and adjacent region to compensate for the superior obliquity of the femur.


The fibula is located on the adjacent section of the tibia, where it is connected to the tibia both above and below. It is the minor among the two-leg bones and also in ratio to its dimension; it is the slimmest of all elongated bones.

Short Bones

The section of the bone that is projected for strength and joined with restricted movement is called the proximal phalange. It is created of several small bones i.e. the carpus and tarsus. These contain cancellous tissue protected by a thin crust of compact substance. The patella is composed of additional sesamoid bones.

Also Read: Number of Bones in Human Body

Short Bones of Upper Extremity


The carpal bones, eight in number. They are organized in two rows. Those of the proximal row, beginning from radial to ulnar side, are termed as the scaphoid, lunate, triquetrum, and pisiform. Those of the distal row, in a similar direction, is called the trapezium, trapezoid, capitate, and hamate.


These are made up of five cylinder-shaped bones that are put together on the opposite side. The fibula is located on the adjacent section of the tibia, where it is connected to the tibia both above and below. Medial, lateral, and dorsal are the three surfaces.


The phalanges are fourteen in count i.e., three for all fingers, and two for the thumb. Each contains a body and two boundaries. The body points from overhead descending are curved posteriorly, concave in front from directly above descending, level from side to side; its edges are irregular which give extra strength to the fibrous covers of the Flexor tendons.

Short Bones of Lower Extremity


The calcaneum, talus, cuboid, navicular, and the first, second, and third cuneiforms are the seven tarsal bones.


The metatarsus is made up of five bones that are numbered from the medial to the lateral sides. The body is prismoid in form, points progressively from the tarsal to the phalangeal extremity, and is bent longitudinally, to be curved below, and slightly convex above.


The phalanges of the foot resemble, in digit and overall organization, with the hand. The great toe has two, and the other toes each have three. They fluctuate from them, though, in their size, the forms being much condensed in measurement, and, particularly in the first row, laterally compacted.


With the help of a longitudinal bar known as the sternal plate, the ventral ends of the ribs become linked to one another, and these sternal plates fuse in the middle line to form the manubrium and body of the sternum, opposite the first seven pairs of ribs.

The sternum is an extended, compressed bone, making the central part of the frontal wall of the thorax. Its higher termination maintenances the clavicles, and its borders articulate with the cartilages of the first seven sets of ribs. The manubrium, the body or gladiolus, and the xiphoid process are the three parts that constitute the xiphoid process.


The posterior half of the shoulder girdle is formed by the scapula. The scapula, or shoulder blade, is a big triangular-shaped flattened bone. It is located in the posterior-lateral part of the thorax. The shoulder bone is thin, fragile, and can be easily broken.

Irregular Bones

The uneven bones are like commencing their irregular form, will not be gathered under the previous heads. They consist of cancellous tissue surrounded inside a thin layer of compressed bone. The vertebrae, sacrum, coccyx, temporal, sphenoid, ethmoid, zygomatic, maxilla, mandible, palatine, inferior nasal concha, and hyoid are among the uneven bones.


The vertebral column is made up of a collection of bones called vertebrae and is flexuous and flexible. There are thirty-three (33) vertebrae in total, which are classified as cervical, thoracic, lumbar, sacral, and coccygeal, depending on the regions they occupy. The cervical region has seven, the thoracic region has twelve, the lumbar region has five, the sacral region has five, and the coccygeal region has four. True or moveable vertebrae are the vertebrae in the upper three sections of the spinal column that stay differentiated throughout life. False or fixed vertebrae are those in the sacral and coccygeal areas, which are joined together in the adult to create two bones—five forming the higher bone or sacrum. The terminal bone, or coccyx, is made up of four bones.


The sacrum is a huge, tri-lateral bone, located in the inferior portion of the vertebral column and at the higher and posterior portion of the pelvic cavity. It is implanted like a wedge among the two hip bones. Its superior part or base articulates with the last lumbar vertebra and at its tip with the coccyx.


The coccyx is usually made up of four basic vertebrae. The numeral may though be greater than before to five or make lesser to three. All three parts that are outlined have a fundamental body and articular corner to corner progressions; the preceding piece (occasionally the third) is an ordinary nodule of bone. All the parts are destitute of pedicles, laminae, and spinous progressions.


The skull is a bony structure that covers and protects the brain. In an adult, 8 cranial bones are fused using sutures. Anatomically, on the joint of the vertebral column, an oval-shaped, skull is positioned which is broader behind than in anterior. It is separable into two portions:

  1. Cranium
    • Occipital
    • Two parietals
    • Frontal
    • Two temporal
    • Sphenoidal
    • Ethmoidal
  2. Facial
    • Two nasal
    • Two maxilla
    • Lacrimal
    • Zygomatic
    • Palatines
    • Two lesser nasal conchae
    • Vomer
    • Mandible

Hyoid Bones

It is also positioned at the core of the tongue and linked to the bottom of the skull by the ligament. A detailed description of each cranium bone is disused below:

Occipital Bones

It is located at the posterior and inferior portion of the cranium, is trapezoid in shape, and bent on itself. It is perforated by a large oval aperture called the foramen magnum, which connects the cerebral cavity to the spinal canal.

The Parietal Bone

The side and top of the skull are formed by the combination of the parietal bones. Every bone is irregular four-sided in arrangement and has two planes, four boundaries, and four angles.

The parietal articulates with five bones:

  1. Opposite Parietal,
  2. Occipital
  3. Frontal
  4. Temporal
  5. Sphenoid

The Frontal Bone

The frontal bone looks like a cockle-shell in arrangement and comprises of two portions perpendicular part, the squama in relation with the area of the forehead; and an orbital or straight part, which goes into the creation of the roof of the orbital and nasal cavities.

Facial Bones

• Nasal Bone

The nasal bones have dual minor oblong bones, variable in magnitude and arrangement in dissimilar persons. They are positioned along sides at the central and upper part of the face, by their intersection at “the association” of the nose.

• Maxillae Bone

The maxillae are the chief bones of the face, except the mandible, and arrangement, by their combination constitutes the entirety of the higher jaw. All of these factors contribute to the formation of the borders of three cavities: the roof of the mouth, the ground and sidewall of the nose, and the ground of the orbit. It also arrives into the creation of two fossae, the infratemporal and pterygopalatine, and two fissures, the lesser orbital and pterygomaxillary. All bone contains a body and four processes—zygomatic, frontal, alveolar, and palatine.

• Lacrimal Bone

The lacrimal bone, the minutest and most fragile bone of the face, is located at the obverse portion of the medial wall of the orbit. There are two sides and four boundaries.

• Zygomatic Bone

The zygomatic bone is a tiny, quadrangular bone that creates the prominence of the cheek, a portion of the lateral wall and floor of the orbit, and portions of the temporal and infratemporal fossae in the upper and lateral area of the face. It has four processes: front-sphenoidal, orbital, maxillary, and temporal, as well as four boundaries and a malar and temporal surface.


Although the vomer is in the middle plane, the anterior portion is usually bent to one side or the other. It is a thin, quadrilateral-shaped structure that constitutes the nasal septum’s hinder and lower parts.


Sutures are defined as junctions or lines of articulation between adjacent bones of the skull. Sutures are fibrous joints that can only be found in the skull or cranium. Sharpey’s fibers bind them all together. Sutures allow for a small amount of movement, which contributes to the skull’s elasticity.

Types of sutures present in the skull:
1) Coronal suture
2) Lambdoid suture
3) Sagittal suture
4) Frontal/ Metopic suture
5) Occipito-mastoid sutures
6) Parieto-mastoid suture
7) Spheno-frontal suture
8) Spheno-parietal suture
9) Spheno-squamosal suture
10) Spheno-zygomatic suture
11) Squamosal suture
12) Zygomatico-temporal suture
13) Zygomatico-frontal suture

Human skull side sutures right
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