Ribs and Sternum - Anatomy & Physiology

BACK TO MUSCULOSKELETAL ANATOMY AND PHYSIOLOGY

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: