Osteology

• The bones of the thoracic limb include the scapula, humerus, radius and ulna, carpal bones, metacarpal bones, phalanges, and sesamoid bones

  
• Scapula


  • Medial surface (costal surface) - medial side of the bone
  • Lateral surface

  
• Scapula - Medial surface (costal surface)


  • Serrated face - the dorsal aspect of the costal surface (where the serratus ventralis muscle attaches)
  • Subscapular fossa - the ventral aspect of the costal surface (where the subscapularis muscle attaches)
• Scapula - Lateral surface


  • Spine - the ridge on which the trapezius and deltoideus are attached
  • Supraspinous fossa - the depression craniodosal to the spine
  • Infraspinous fossa - the depression caudoventral to the spine
  • Cranial, caudal and ventral angles - the three corners of the triangular shape
  • Cranial, caudal and dorsal borders - the three sides of the triangular shape
  • Acromion - the distal extremity of the spine
  • Neck - the constriction near the ventral angle
  • Infraglenoid tubercle - the roughened area the caudal aspect of the neck
  • Supraglenoid tubercle - the projection near the ventral aspect of the cranial border
  • Corocoid process - the projection at the cranial aspect of the ventral angle
  • Glenoid cavity - the articular surface at the ventral angle
  • Scapular cartilage - a cartilaginous extension of the dorsal border

  
• Scapula - Comparative features

  • The shape of the scapula is more or less triangular, with this being more so in the ungulates than the carnivores
  • The acromion is absent in some domestic species, while it forms the hamate process in the carnivores
  • Cats have an additional projection, the suprahamate process
• Humerus


  • Head - the rounded, proximal end which articulates with the glenoid cavity
  • Neck – the head is separated from the body by the neck
  • Greater tubercle - on the proximal, craniolateral aspect
  • Lesser tubercle - on the proximal, medial aspect
  • Intertubercular groove - located between greater and lesser tubercles
  • Tricipital line - located on the lateral side
  • Deltoid tuberosity - where the deltoideus muscle is attached
  • Brachial groove - on the lateral surface, distal to the deltoid tuberosity
  • Teres major tuberosity - roughened area on the medial side
  • Condyle - the whole distal end of the humerus
  • Capitulum - the lateral part of the articular surface of the condyle
  • Trochlea - medial part of the articular surface of the condyle

  
• Radius


  • Head - the proximal epiphysis, which has the the fovea capitis that articulates with the humeral condyle
  • Neck – the part adjacent to the head
  • Body – compressed to form cranial and caudal surfaces
  • Trochlea - the distal epiphysis, which has a concave carpal articular surface and the (radial) styloid process on the medial side

  
• Radius - Comparative features

  • The radius and ulna remain separate and distinct in the pig and carnivores but they fuse in the ruminants and horse
  • In the ruminants, the two bones can be easily differentiated even though they are fused, but in the horse, they blend indistinguishably
• Ulna


  • Olecranon - the proximal extremity, which is proximal to the trochlear notch; has the olecranon tuber and the anconeal process
  • Trochlear notch - articulates with the humerus; at its distal end are the medial and lateral coronoid processes
  • Body – initial part compressed laterally, middle part is three-sided, and the distal part is irregular in shape; has a rough interosseous border
  • Head - the distal end; articulates with the radius medially; has a prominent (ulna) styloid process laterally part of which articulates with carpal bones

  
• Ulna - Comparative features


  • In the horse and ruminants, the ulna fuses to the radius
  • In the horse, the ulna styloid process becomes indistinguishable from the radius after the two bones fuse
  • The equine radius is considered to have medial and lateral styloid processes

  
• Carpal bones


  • The carpus includes small, irregular bones arranged into two rows
  • The general carpal bone pattern consists of eight units in two rows with named bones forming the proximal row and numbered bones forming the distal row
• Carpal bones


  • Radial carpal bone (Cr)
  • Intermediate carpal bone (Ci)
  • Ulnar carpal bone (Cu)
  • Accessory carpal bone (Ca)
  • First carpal bone (C1)
  • Second carpal bone (C2)
  • Third carpal bone (C3)
  • Fourth carpal bone (C4)

  
• Carpal bones - Comparative features

  • The pig has the generalized pattern of 8 separate bones
  • In carnivores the radial and intermediate bones fuse to form the intermedioradial carpal bone. They have 7 separate carpal bones
  • In ruminants, the first carpal bone is absent. The second and third carpal bones are fused. They have 6 separate carpal bones
  • The horse may have 7 or 8 carpal bones. The first carpal bone is often absent. Rare individuals have a fifth carpal bone

  
• The basic pattern for the skeleton of the mammalian manus consists of five comparatively equal rays, each comprising a metacarpal bone and proximal, middle, and distal phalanges

  
• Manus skeleton evolution


  • This has been modified for cursorial locomotion (running) in all domestic species
  • The manus (and pes) has been raised from the plantigrade ("flatfooted") posture which is seen in animals such as the bear
  • The digitigrade posture of dogs and cats is an intermediate stage; these animals support themselves by the digits
  • All ungulates (ruminants, pigs, and horses) have an unguligrade posture, where only the tips of digits protected by hooves (ungulae) provide support
  • During this evolutionary process, the abaxial digits first lose permanent contact with the ground and the remaining digits are adapted to carry an increased proportion of the weight
  • This process has progressed to various degrees in the domestic animals
  • Dogs and cats have four functional digits, pigs and ruminants have two functional digits, and only the third ray remains functional in the horse
• Metacarpal bones


  • Base - the proximal extremity with a flat articular surface for the distal row of carpal bones
  • Body - the shaft (diaphysis)
  • Head (Caput) - the distal extremity; articulates with the proximal phalanx

  
• Metacarpal bones - Comparative features

  • The carnivores have the generalized pattern of five metacarpal bones
  • The pig has four metacarpal bones, with the first being absent
  • In the ruminants, the single metacarpal bone is formed by fusion of the third and fourth bones to form the cannon bone. The first and second metacarpal bones are absent and the fifth is markedly reduced
  • In the horse, the third metacarpal bone is larger than the second and fourth metacarpal bones and it is the only one which supports a digit. The first and fifth metacarpal bones are absent

  
• Digits


  • The proximal phalanx is a short cylindrical bone with a proximal extremity that articulates with the head of the metacarpal bone and a distal articulation in the form of a shallow trochlea
  • The middle phalanx is shorter than, but basically very similar to, the first phalanx
  • The distal phalanx corresponds to the form of the hoof or claw in which it is wholly (hoof) or partly (claw) contained

  
• Distal phalanx


  • Extensor process - where the extensor tendons terminate
  • Flexor tubercle – where the deep digital flexor tendons insert

  
• Digits - Comparative features

  • Carnivores have four weight-bearing digits and the first digit is typically reduced (dewclaw). The first digit contains only two phalanges
  • In the pig, has two weight-bearing digits (third and fourth), two paradigits (second and fifth), and the first digit is missing
  • Cattle have two weight-bearing digits (third and fourth), two paradigits (second and fifth), and first digit is absent
  • The horse has only one digit (the third)
• Distal phalanges - Comparative features

  • Carnivores: Ungual crest, Ungual process
  • Ungulates: No specific features mentioned
• Sesamoid bones


  • There are two proximal sesamoid bones on the palmar aspect at the metacarpophalangeal joint of each major digit
  • There is a single distal sesamoid bone on the palmar aspect of each distal interphalangeal joint

  
• Sesamoid bones - Comparative features

  • Carnivores: Has single proximal sesamoid bone, Distal sesamoid bone is cartilaginous
  • Horse: The distal sesamoid bone is known as the navicular bone
  • Pig: The distal sesamoid bones are absent
  • Ruminants: Similar to the horse

  
• Thoracic cage


  Bony cage formed by the sternum, ribs, costal cartilages and the bodies of the thoracic vertebrae
• Thoracic cage


  • Protects the thoracic organs
• Thoracic vertebrae


  Part of the thoracic cage
• Thoracic vertebrae


  • Short bodies
  • Long spinous processes
  • Short transverse processes
  • Articular facets
• Body of thoracic vertebrae

  • Thick ventral portion of the vertebra
  • Cranial extremity - convex
  • Caudal extremity - concave
• Vertebral arch


  • Dorsal part which surrounds the spinal cord
  • Subdivided into pedicle and lamina
• Vertebral foramen


  Space formed by the vertebral arch and the body
• Spinous process


  Single prominence projecting dorsally from the arch
• Transverse processes


  Lateral extensions of the vertebral arch
• Articular processes


  Paired cranial and caudal processes located at the junctions of the laminae and pedicles
• Cranial and caudal intervertebral notches


  Indentations on each side of the arches that form intervertebral foramina for emergence of spinal nerves
• Costal fovea


  Two facets for articulation with the head of the rib, located on the cranial and caudal end of the vertebral bodies
• Transverse costal fovea


  Facet on the transverse process which articulates with the tubercle of the same numbered rib
• Ribs


  Long curved bones forming the lateral wall of the thorax
• Head of rib


  Articulates with caudal and cranial costal fovea of adjacent thoracic vertebrae and the intervertebral disc
• Tubercle of rib


  Articulates with the transverse process of the same numbered vertebra
• Body of rib


  Curved and thick