BONES (COMPARATIVE ANATOMY)

• Bones are hard, semi-rigid, calcified connective tissue that form the skeleton, support and protect vital organs of the body, and serve as levers for muscular action.
• The shapes of bones include long bones (ossa longa), short bones (ossa brevis), and flat bones (ossa plana).
• Long bones are found mainly in the limbs, have a body/shaft called diaphysis and two ends called the epiphyses, and weigh less than short bones.
• Short bones are associated with the spread of pressure exerted in the regions of the wrist and ankle, and are found in the carpal (wrist) and tarsal (ankle) areas.
• Flat bones are found in the thoracic and pelvic girdles and in the head, weigh less than long bones, and are irregular in shape.
• Irregular bones are part of the vertebral column and bones of the skull, are for muscular and ligamentous attachment, and have projecting processes.
• Bones can be classified according to their structure into cancellous or spongy bone and compact bone.
• The diaphysis and epiphyses of long bones, the medullary cavity, and the cortex of compact bone are parts of the bone.
• The periosteum is a layer of specialized connective tissue covering the outer surface of the bone.
• The hindlimb skeleton has significant features such as the hipbone firmly fixed to the vertebral column, no ventral union between the two hipbones, and no independent tarsus.
• The wing skeleton may be divided into the shoulder girdle which includes the Scapula, Coracoid, and Clavicle (wishbone/furcula), and the wing which includes the Upper arm, Forearm, and Manus or hand.
• The third to the sixth ribs have two segments: a Vertebral segment and a Sternal segment.
• All except the first and last ribs have uncinate, adding strength to the thoracic cavity.
• The leg skeleton may be divided into the Pelvic girdle or hip bones which include the Ileum, Ischium, and Pubis or pin bones, and the leg which includes the Femur or thighbone, Tibia and fibia, and Pes or foot which includes the Tarsus, Metatarsus, and Digits or toes.
• The ribs are seven pairs, with the first, second, and sometimes the seventh not reaching the sternum.
• The sternum, or breastbone, is a complex shape and has been described as a quadrilateral, curved plate with processes projecting from each angle and from the middle of the cranial and caudal borders.
• The skull is divided into two regions: the Rounded cranium and the Conical facial region.
• The last of the coccygeal are fused to form the pygostyle and provides a strong foundation for the tail feathers.
• The last thoracic vertebra is located in the caudal region, while the sacral and lumbar regions are located in the thoracic area.
• The endosteum is a thin fibrous membrane that lines the medullary cavity and osteonal (Haversian) canals of a bone.
• Physitis is the inflammation of the growth plates in the long bones of growing foals.
• Ruminant metacarpal bones have 2 metacarpal bones, the 1st and 2nd (McI and McII) are missing and the 3rd and 4th are fused, the common name for the fused metacarpal bones III and IV (McIII and McIV) is large metacarpal bone, the common name for the greatly reduced metacarpal bone V (McV) is small metacarpal bone.
• Horse metacarpal bones have 3 metacarpal bones, the 1st and 5th are missing, the common names for the greatly reduced metacarpal bones II and IV (McII and McIV) are splint bones, the common name for the large metacarpal III (McIII) is cannon bone, it is the only metacarpal bone to articulate with the digit.
• Pig digits have 4 digits, the 1st is missing, the 2nd and the 5th are reduced and do not bear weight and are called dew claws, they are fully formed except that they lack a distal sesamoid bone.
• Bone processes, depressions, and openings are parts of the skeleton.
• The 3rd and 4th digits in ox are fully developed weight-bearing digits consisting of 3 phalanges and 3 sesamoid bones.
• Pig metacarpal bones have 4 metacarpal bones, the 1st metacarpal bone (McI) is missing, metacarpal bones II and V (McII and McV) are greatly reduced and don’t bear weight, the weight is borne by metacarpals III and IV (McIII and McIV).
• The skeleton can be divided into three major groups: axial (skull, vertebral column, ribs & sternum), appendicular (thoracic & pelvic limbs), and visceral (baculum or os penis, ossa cordis, os rostri).
• Ox have 4 digits, 2 weight-bearing and 2 non-weight-bearing, the 1st digit is missing, the 2nd and 5th digits are vestiges externally manifested as horny dew claws behind the fetlock.
• Metacarpal I (McI) is much reduced, bears no weight, and has one associated sesamoid bone.
• The main digits (3rd and 4th) in pig consist of 3 phalanges, 2 proximal sesamoids and 1 distal sesamoid.
• Common sites of luxation in horses include the stifle/patella, hock, fetlock, and pastern.
• The dew claw is part of the metacarpal bone.
• Horse digits have one digit per limb supporting Mc III.
• Osteochondrosis is a condition that affects the growth of cartilage and bone in the joints of horses.
• Osteochondritis dissecans (OCD) is a relatively common developmental disease that affects the cartilage and bone in the joints of horses.
• Osteochondrosis is a condition that causes clinical signs of disease in 5 - 25% of all horses and can occur in all horse breeds.
• Osteochondrosis is common in giant and large breeds of dogs such as Great Danes, Labrador Retrievers, and Rottweilers.
• Cephalic index (CI) is the ratio of the maximum width of the head (A) multiplied by 100 divided by the head’s maximum length (B).
• Frontal sinuses occupy the dorsal (top) part of the skull, between the eyes.