Ribs and Sternum - Anatomy & Physiology
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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
- 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)
- Three openings:
- 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: