Classification of bones Any bone may be classified into one of the following groups:

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1 Skeletal system This system is made up of hard tissues like bone and cartilages. This system gives form and shape to animal body The skeleton of a living animal is made up living structures of bones. The bones have blood vessels, lymphatic vessels and nerves. They are subject to disease, repair themselves and adjust to changes during stress. Functions of Bones: Protection: protection of some vital organs from the external damages is one of the important functions of bones. The central nervous system (CNS) is protected by the skull and vertebral column; the heart and lungs by rib cage; and pelvis protects the internal parts of urogenital system. Rigidity and form to the body: animals without a skeleton of some type have little or no regular form. The skeleton gives a basis for the external structure and appearance of most animals. Act as lever: in the vertebrates, locomotion, defense, offense, grasping, and other activities of this type depend largely upon the action of muscles that are attach to the levers. Almost without exception, these levers are made of bone and are integral parts of skeleton. Storage of minerals: the entire skeleton serves as a dynamic storage area for minerals, particularly calcium and phosphorous. These minerals are deposited and withdrawn as needed in the on-going homeokinetic process. Site for blood formation: blood formation is not strictly a function of bone proper, but of the marrow found within the marrow cavity of long bones and within the spongy substance of all young bones. Classification of bones Any bone may be classified into one of the following groups: Long bones: are relatively cylindrical in shape with two extremities called epiphyses (see Figure ). There is metaphysis between each epiphysis and the diaphysis. A long bone grows in length only at the epiphyseal cartilage which is located within the metaphysis. Epiphysis Metaphysis Diaphysis Medullary Cavity Epiphysis Metaphysis Figure 7: longitudinal section of the humerus of a mature dog. Anatomy/Skeletal system/pj 08 1

2 Function of long bones: chiefly as levers and aid in support, locomotion and prehension. The best examples of long bones are pectoral limb, humerus, radius, ulna, metacarpals, phalanges; pelvic limb, femur, fibula, tibia, metatarsals and phalanges. Short bones: are somewhat cuboid in shape i.e approximately equal in all dimensions. There is no marrow cavity. They are found in complex joints such as the carpus (knee) and tarsus (hock). Example of short bones: Patella. Function: - for variety of movement - absorption of shock Flat bones: are relatively thin and expanded in two dimensions. They consist of two plats of compact substance, lamina externa and lamina interna, separated by diploe. Example of flat bone: frontal base of skull, scapula and pelvic bones Functions: - protects vital organs such as brain, the heart and lungs. - many provide large areas for muscle attachment. Sesamoid bones: they are developed along the course of tendons. Example: Patella (knee cap) is the largest sesamoid in the body. Functions: - reduces friction or change the course of tendons. - may change the angle of the pull of muscles and this give a greater mechanical advantage. Phunumatic bones: they contain air spaces or sinuses that communicate with the exterior. Example: long bones of bird, frontal bones and maxillary bones of the skull. Irregular bones: are unpaired bones located on the median plane and include the vertebrae and some of the unpaired bones of the skull. Functions: - protection, support and muscle attachment. For better understanding the skeletal system can be divided into two parts viz the axial skeleton and appendicular skeleton. Axial skeleton: is made up of skull, and vertebral column sternum and ribs. The table below indicates the bones of the axial skeleton by regions. Anatomy/Skeletal system/pj 08 2

3 Table: Bones of the Axial skeleton system. (Source: Spurgeon, 1992) Skull Cranial bones -occipital - parietal - interparietal - temporal - frontal - ethmoid - sphenoid Facial bones - pterygoid - lacrimal - nasal - palatine - conchae (turbinates) - maxilla - incisive (premaxilla) - zygomatic (malar) Vomer Mandible Hyoid Vertebrae cervical thoracic lumbar sacral caudal Ribs True ribs -join sternum by costal cartilages False ribs- not directly connected with sternum Floating ribs- last 1 or 2 pair connected only with vertebrae Sternum manubrium body xiphoid process Skull: forms the basis of the head. It consists of cranial bones, which surround the brain and facial bones, which exhibits observable variation among the species. Function: - protection of brain - Supports many sense organs - Forms passage for the beginning of digestive and respiratory system Vertebral column: composed of median, unpaired and irregular bones. The following indicates the part of vertebral column and letters are used to designate the respective regions. Cervical vertebrae (C) - neck region Thoracic or dorsal (T) - chest region Lumbar (L) - loin region Sacral (S) - in region of pelvis- fused vertebrae Fused Lumbar and Sacral (LS)- in fowl Caudal or Coccygeal (Cd) - located in tail Anatomy/Skeletal system/pj 08 3

4 Vertebral formula: for a given species consist of the letter symbol for each region followed by the number of vertebrae in that region in the given species. The following shows the vertebral formula of common farm animals. Cow: C7 T13 L6 S5 cd18-20 Sheep: C7 T13 L6-7 S4 cd16-18 Pig: C7 T14-15 L6-7 S4 cd20-23 Horse: C7 T18 L6 S5 cd15-20 Chicken: C14 T7 LS14 cd6 Sternum and Ribs: forms the floor of the bony thoracic wall and gives attachment to the costal cartilages of the sternal (true) ribs as well as forming a place of origin for the pectoral muscles. The sternum consists of segments called sternebrae which tend to fuse together as age advances. The number of sternebrae varies with species as follows: Pig: 6; Sheep: 6; Cow: 7; Goat: 7; Horse: 8 Sometimes the last one or two pair of ribs have no connection with other ribs at the ventral end. Such ribs are called floating ribs. The spaces between the ribs are called intercostal spaces. Figure below shows the Axial skeleton of cattle Cervical Thoracic Sacrum Lumbar Skull Coccygeal Ribs 2.2. Appendicular skeleton: is made up of the bones of the limbs. Table below compares the bones of the front (pectoral) limb to that of the hind (pelvic) limb by region. Table: Comparison of Pectoral and Pelvic bones (Source: Spurgeon, 1992). Pectoral limb Pectoral girdle (shoulder girdle) Scapula Clavicle Coracoid Humerus-arm Pelvic limb Pelvic girdle (os coxae)-pelvis Ilium Ishium Pubis Femur- thigh Anatomy/Skeletal system/pj 08 4

5 Radius-forearm Ulna- forearm Carpus- Metacarpus- cannon Phalanges- digits Patella Tibia- leg Fibula- Tarsus- hock Metatarsus- cannon Phalanges- digits Pectoral limbs: Scapula (shoulder blade)- in all animals, it is rather flat, triangular bone. Humerus (arm bone)- is a typical long bone that varies only in minor details from one animal to another. Radius- is the larger of the two forearm bones, and the ulna is the smaller mammal but not in birds. The radius is well developed in all species. Ulna- varies in its degree of development from species to species. In horse the proximal portion of the shaft of the ulna is well developed but fused to the radius. The cow, sheep, goat and pig each have a complete ulna, but with restricted or no movement between the ulna and radius. The cat and dog have considerably more movement between these complete bones, but not nearly as much as man. Carpus- in all animals is a complete region that includes two rows of small bones. Those in the proximal row are called radial, intermediate and ulnar. Those in the distal row are numbered as 1,2,3, and 4. Bones fore limb and hind limb are shown below. Scapula Pelvis Humerus Ulna Radius Carpus Metacarpus Digits Femur Tibia & Fibula Tarsus Metatarsus Digits Bones of fore limb Bones of hind limb Anatomy/Skeletal system/pj 08 5

6 Skeleton of cattle Anatomy of chicken The domestic chicken is descendent of red jungle fowl. All systems are present but there is modification of each system to meet the requirements of species. Modifications are described below: General modification Cattle Chicken 1. Mouth Beak 2. Fore limb wings 3. Long bones with marrow without marrow, pneumatic 4. Lungs and kidneys not attached attached to dorsal wall Presence of comb and wattle in head Anatomy/Skeletal system/pj 08 6

7 Beak Wattle Wing Comb Leg Modification in chicken Skeletal system Is made up of bones that are pneumatic in nature making the body light for flight. Figure below shows bones making skeletal system of chicken Radius & ulna Humerus Pelvic bone Tibia Skull Cervical vertebrae Femur Sternum Metatarsus Skeleton of chicken Skeleton of pig Anatomy/Skeletal system/pj 08 7

8 Skeleton of goat Skeleton of horse Anatomy/Skeletal system/pj 08 8