OSTEOLOGY:
It is the branch of anatomy which deals with the study of bones and cartilages.
The frame work of human body is composed of bony and cartilagenous tissue called Skeleton. The skeleton is of two types:
1.Exo-skeleton: It is that part of skeleton which is present in relation with the skin, e.g., Enamel of tooth.
2.Endoskeleton: It is deeply situated and forms main skeleton of human beings. It is subdivided into two sub-varities.
Visceral Endoskeleton :
(i)It is found in relation with certain viscera, e.g.,
(ii)OS Cordis: It is seen in heart of Ox.
Bacculum:
It is present in between the corpora cavernosa of many cornivores, e.g., Dog, Bear, Tiger, Monkey, etc.
(a) Bones of visceral arches, e.g., Mandible, hyoid bone, ear ossicles.
(b) Somatic Endoskeleton:
Almost all bones of the body belong to this variety.
FUNCTIONS OF BONES:
Bone is a rigid, highly vascular (c.f. cartilage), dynamic, constantly changing, mineralized Connective Tissue. It performs following functions:-z
- These help in SPEECH, i.e., Mandible; hyoid bone; bones of palate.
CLASSIFICATION OF BONES:
Bones can be classified as follows:-
Developmental Classification:
Intramembranous: Here the embryonic mesnchyme directly differentiates into bony tissue. It usually occurs in embryo, in case of those bones which are urgently required for support or protection. The characteristic of this type of bone formation is its rapidity of formation.
Bones of the vault of the skull. Bones of the face.
Clavicle:
Subperiosteal bone formation. (It should be noted that growth in thickness of cartilage bone, i.e. subperiosteal ossification is by process of intramembranous ossification).
Intracartilagenous :
Here first of all cartilagenous model of bone is formed which later on transforms into bony tissue. It is an altogether more leisurely affair.
Examples:
| Description |
|---|
| All long bones of the body except the clavicle. |
| Short bones. |
| Irregular bones. |
Membrano – cartilagenous :
Example:
At the junction of vault and base of skull the bones are formed by this method.
a) Thoracic
b) Lumbar
c) Sacral
d) Coccygeal
e)Ribs
f) Sternum
2. Appendicular bones:
Examples:
i) Bones of upper limb
ii) Bones of shoulder girdle (girdle means ring).
iii) Bones of lower limb
iv) Bones of hip girdle :
IV. Classification according to size & shape:
Long Bones: They show the following characteristics :-
i)Two ends (Epiphyses).
ii) Shaft
iii)Long Size
Example:
a) Humerus, ulna, radius.
b) Femur, tibia, fibula.
II.Structural Classification or architectural classification: According to this mode of classification, there are two types of bones:–
1.Compact bone (Haversian bone): Here well developed Harversian lamellae or cylindrical lamellae are seen. The lamellae consist of collagen fibres, lying in a calcified material; adjacent lamellae are held together by interchange of fibres. Bone-cells lie scattered between the lamellae.
Examples:
i)Shafts of long bones.
ii)Outer and inner tables of the skull bones.
Spongy bone (Cancellous bone): Here the lamellae are arranged flat. No typical Haversian systems are seen.
Example:
i)Ends of long bones
ii)Diploe of skull
Regional Classification (Total 206 bones):
Axial bones (Total 80):
Examples:
i) Skull:
a) Cranium and facial bones
b) Hyoid bone
c) Ear ossicles
d)Vertebrae :
e) Cervical
2.Long-short bones (Miniature long bones): They show the following characteristics :
Two ends.
i)Shaft
ii)Short in length
Examples:
i)Metacarpal bones
ii)Bones of hand
iii)Phalanges
iv)Bones of foot
Short bones: They are small in size and have various shapes. Examples:
i) Carpal bones (Bones of the hand -8 in number) ii) Tarsal bones (Bones of the foot – 7 in number). Flat Bones: They are characterized by two thin plates of compact bone, between which lies a variable quantity of spongy bone. They resemble sandwiches.
Examples:
Scapulae.
ii) Sternum.
iii) Ribs.
iv) Most of the skull bones.
Irregular bones: Here the bones are irregular in shape. Example:
i) Vertebrae
ii)Hipbone
iii)Sphenoid bone
iv) Maxilla bone
Miscellaneous Classification :
1.Sesamoid bones (it means seed like – Arabic word):
These are the bones which develop in tendons :-
Examples:
Patella (It is the largest bone which develops in the tendon of quadriceps femoris).
Pisiform bone (It develops in the tendon of flexor carpi ulnaris muscle).
Un-named sesamoid bones: They develop in the tendons of following muscles:
a)Flexor hallucis brevis
b)Adductor pollicis brevis
c)Flexor pollicis brevis
d)Tibialis posterior (Behind the navicular tuberosity)
e)Peroneus longus (on the side of the cuboid bone)
f)Gastrocnemius (in lateral head).
Supernumery bones (Extra Bones):
They most commonly develop in relation with appendicular skeleton due to traction or pressure on a particular part :
Accessory bones:
They usually develop in relation with axial skeleton, e.g.,
i)Cervical rib
ii)Lumbar rib
iii)Bipartite patella
iv)Two frontal bones
v)Two piece – 5th lumbar vertebra