The bones entering into the supportive structure of the body are held in close relation with each other by means of ligaments and muscles. Thus the skeleton consists of a strong, firm framework, possessing all manner of movements due to the action of the attached muscles and the leverage of the bones, allowed by the ligaments holding the bones in relation with one another. The body skeleton consists of two hundred and six bones, as follows: Vertebral column 26 Skull 22 Hyoid bone 1 Ribs and sternum 25 —74 AppendicularfUpper limb 64 skeleton \Lower limb 62 —126 Auditory ossicles (bones of ear) 6 Total 206 The patellae, two in number, are included in this list, but not the sesamoid bones. The latter are small bones (shaped like sesame seed) found embedded in tendons covering the knee, hand, and foot. Classes of Bones. — Bones are divisible into four classes: long, short, flat, and irregular. Long Bones. — These are found in the limbs, they support the weight of the trunk and form a system of levers which permit the power of locomotion and prehension. Long bones possess a shaft and an upper and lower extremity. The shaft or the diaphysis is cylindrical, containing in the centre a hollow cavity, the medullary canal, in which during life is the bone-marrow. Surrounding this is dense compact tissue of considerable thickness, but not so thick near the extremities. The extremities or epiphyses are usually expanded to enable one bone to articulate with another and to afford attachment of muscles. They are usually developed from separate centres of ossification called epiphyses. Examples of long bones are the femur or thigh bone, the humerus or bone of the arm, the clavicle or collar bone, the radius and ulna (bones of the forearm), the tibia and fibula (bones of the leg), the metacarpal, metatarsal, and phalanges (the small bones of the hand and foot) respectively. Short Bones. — These are found in that portion of the body where strength and compactness are required and the motion of the part is limited, as the bones of the carpus (wrist) and tarsus (instep). These bones consist of cancellous tissue covered by compact bone. They are held firmly together by ligaments. Some include the patellae and sesamoid bones under this variety. Flat Bones. — ^These are found wherever protection is required, or a broad surface for the attachment of muscles is essential, as the bones of the skull and the scapulae (shoulder-blade) . Flat bones are composed of two thin layers of compact tissue, between which is a variable amount of cancellous tissue. In the bones of the skull these layers of compact tissue are termed the tables of the skull ; the innermost is thin and called the vitreous table. The cancellous tissue between the layers is called the diploe. The flat bones are the occipital, parietal, frontal, nasal, lacrymal, vomer, scapula, sternum, ribs, and some authors include the patella. Irregular Bones. — These are of varying shapes which cannot be classified under any of the preceding groups. They consist of a layer of compact tissue externally enclosing cancellous tissue. The irregular bones are : the vertebr8e, sacrum, cocc3rx, temporal, sphenoid, ethmoid, malar, maxilla, mandible, palate, turbinates, and hyoid. Surfaces of Bones. — The examination of a bone will show numerous depressions and elevations upon its surface, which for purposes of study have been classified into the following eminences and depressions: (1) articular; (2) non-articular. Examples as follows: Articular. — Eminences [Head of humerus. Depressions [Acetabulum of Glenoid cavity of scapula. OS innominatum. Non-articular. — Eminences Depressions Tuberosity is a broad, rough, uneven elevation. Tubercle is a small, rough prominence. Spine is a sharp, slender, pointed eminence. A ridge, line, or crest are narrow, rough elevations along the surface. Notches. Fossae. Grooves. Furrows. Fissures. All are of variable form. The articular eminences and depressions are the extremities and cavities of bones which enter into the formation of joints respectively. The non-articular eminences are to increase the surface of the bone for the attachment of muscles and ligaments; the depres- sions usually receive, hold, or keep in position tendons or muscles, and transmit bloodvessels and nerves. Composition and Structure of Bone. — Bone in the fresh state is pale pink in color, when dried it is grayish white. The constituents of dried bone are 31 per cent organic matter and 69 per cent inorganic matter. The former is represented by bloodvessels and connective tissue, and proteins, such as collagen, ossein, elastin; the latter by mineral salts, e.g., tricalcium and magnesium phosphate, calcium carbonate, and some soluble salts. These ingredients may vary with the age of the individual. Thus in the child there is an increase in the organic matter over the mineral constituents, while the mineral salts predominate in bones of the adult. This absence of salts in the bones of children accounts for the elasticity of the bones, and when fractured they bend rather than break after an injury. This can be seen when a fractured limb, exposed to the X-rays, will appear as a twig bent, but no distinct break is seen (this is termed a green-stick fracture). On the other hand in extremely old persons there is a tendency to fracture of the bones, due to the increase of mineral salts over the organic constituents, rendering them brittle, and unable to withstand the slightest strain without fracture. Rickets is another example of this decrease in lime salts in the bones. It is a disease occurring in children mostly, characterized by a bending of the long bones, and deformity of the limbs, as a result of insufficient and improper nourishment.
Key Takeaways
- Human skeleton consists of 206 bones classified into four types: long, short, flat, and irregular.
- Long bones are found in the limbs and support body weight; they have a shaft with an upper and lower extremity.
- Flat bones provide protection (e.g., skull) or broad muscle attachment surfaces.
Practical Tips
- Understanding bone structure helps identify fractures based on location and type of injury.
- Recognize signs of rickets in children, indicating insufficient calcium intake leading to bone deformities.
Warnings & Risks
- Elderly individuals are at higher risk for brittle bones due to increased mineral salts content.
- Children's bones may bend rather than break upon impact, known as a green-stick fracture.
Modern Application
While the anatomical details remain relevant today, modern medical imaging and diagnostic techniques have advanced significantly. Understanding historical bone anatomy is crucial for recognizing fractures and deformities in emergency settings where advanced diagnostics are unavailable.
Frequently Asked Questions
Q: What are the four main classes of bones?
The four main classes of bones are long, short, flat, and irregular.
Q: How does bone composition differ in children compared to adults?
In children, there is an increase in organic matter over mineral constituents, while in adults the mineral salts predominate. This difference explains why children's bones are more elastic and bend rather than break when fractured.
Q: What is a green-stick fracture?
A green-stick fracture occurs in children where the bone bends but does not completely break, resembling a twig that has been bent without breaking. This type of fracture is due to the higher organic content and lower mineral salts in children's bones.