Ribs and Sternum - Anatomy & Physiology

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Costae

  • Arranged in pairs and articulate with two successive vertebrae
  • Bony dorsal part, body of rib, and ventral costal cartilage
  • Increase in length, curvature and amount of cartilage craniocaudally
  • Cartilage of last rib may fail to join that of its neighbor: said to be floating
  • Join ventrally on the midline at the Sternum, which is comprised of three parts
    • Manubrium: most cranial, projects beyond the first set of ribs and can be palpated
    • Body: segmented sternebrae joined by cartilage in young animals that is later replaced by bone
    • Xiphoid Cartilage: caudal end that projects between lower ends of costal arches, providing attachment for the linea alba
  • Costal Joints:
    • Costovertebral joint: head of rib articulates with vertebral column, ball and socket with very restricted mobility
    • Costotransverse joint: tubercle articulates with vertebra, sliding joint
    • Costosternal joints:
      • Interchondral joints: asternal ribs, elastic syndesmoses
      • Intersternal joints: impermanent synchondroses

Thoracic Musculature

  • Primarily concerned with respiration
    • Inspiratory muscles enlarge the thoracic cavity
    • Expiratory muscles diminish the cavity and force air out
  • The most important thoracic muscle is the Diaphragm, which separates the thoracic and abdominal cavities
Cat diaphragm- Copyright Uwe Gille
  • Intercostal muscles
    • Dome-shaped, convex on its cranial surface
    • Central tendon forms the vertex
      • Neutral position (between full inspiration and full expiration): 6th rib behind the olecranon
    • Attaches via muscular periphery to the costal arch
    • Three openings:
      • Aortic hilus conveying the aorta, azygous vien, and thoracic duct
      • Oesophageal hiatus conveying the oesophagus, vagal trunks and supplying vessels
      • Caval foramen withing central tendon conveying caudal vena cava
    • Innervated by the phrenic nerve, which arises from the caudal cervical nerves (C5-C7)
    • External fibers run caudoventrally and internal fibers run cranioventrally
    • Each is confined to a single intercostal space
  • Transversus thoracis arises from and covers the dorsal sternum and inserts on sternal ribs close to the costochondral junctions
  • Rectus thoracis covers the ends of the first four ribs in continuation of the rectus abdominus
  • Serratus dorsalis overlies the dorsal aspect of the ribs
  • Innervation of these muscles is supplied by the Intercostal nerves, which are ventral branches of the thoracic spinal nerves

Abdominal Musculature

  • Ventrolateral Muscles: flanks and abdominal floor
    • All muscles join via aponeuroses in the linea alba at midline, which runs from the xiphoid process to the pelvic symphysis via the prepubic tendon, ensheathing the rectus abdominus
    • The External abdominal oblique runs caudoventrally from the lateral surface of the ribs and the lumbar fascia to the linea alba
    • The Internal abdominal oblique runs cranioventrally from the tuber coxae and the thoracolumbar fascia to the linea alba
    • The Transversus abdominus is the deepest muscle of the flank, running dorsoventrally from the inner surface of the last ribs and the transverse processes of the lumbar vertebrae
    • The Rectus abdominus forms a broad band parallel to the linea alba, arising from the ventral costal cartilages and inserting on the prepubic tendon
  • Sublumbar Muscles:
    • Psoas minor: stabilizer of the vertebral column, may also rotate the pelvis at the sacroiliac joint
    • Psoas major and Iliacus: