[4] Axial

• Components:

  1. Notochord
  2. Vertebral column
• Protovertebrae in:

  Haikouella and Haikouichthys
• Ribs articulating with sternum

  True ribs
• Ribs articulating with nothing ventrally

  False ribs
• Sternum + sternal elements

  Rib cage
• Sternum in Anura

  Xiphisternum + Omosternum
• Groups with no sternum

  Turtles, snakes, limbless lizards
• Sternum in mammals

  Sternebrae, manubrium and xiphisternum
• Agnathans

  1. No vertebral elements in adult hagfishes
  2. Arcualia in larval hagfish tails
  3. Small cartilaginous vertebral elements in lampreys
• Label the ff.

  A) Acoelous

  B) Amphicoelous

  C) Procoelous

  D) Opisthocoelous

  E) Heterocoelous

  
• Basic Components:

  • Neural tube - protected by both:
  • [a] neural & interneural arches
  • [b] hemal & interhemal arches
  • Neural arches
  • neural - nearer towards the back of the animal
  • interneural / interhemal arches - articulating arches between arches
  • Intercentrum & procentrum
  • inter - hemal arches
  • for anchoring hemal (ventral) arches
• Regions of the Vertebral Column

  Fish:

  1. Precaudal (Abdominal or Trunk)
  2. Caudal

  Tetrapods:

  1. Cervical - support head & neck
  2. Thoracic - chest area
  3. Lumbars - towards pelvic area
  4. Sacrals
  5. Caudals
• Centra classification

  • Based on number of centra are present
  • [1] Aspondyly - no centra in vertebra
  • [2] Monospodyly - just one centrum
  • [3] Diplospondyly - two centra
  • [4] Polyspondyly - ≥3 centra
  • [b] based on whether elements are joint or separate
  • [1] Aspidospondyly - centra & arches are separate
  • [2] Holospondyly - fused vertebral elements per segment
• Centra classification according to notochord/bond

  • [1] Acoelous - flat ends
  • [2] Amphicoelous - both ends are concave
  • Notochord has greater contribution to vertebral column
  • [3] Protocoelous - concave anterior
  • [4] Opisthocoelous - concave posterior
  • [5] Heterocoelous - saddle shaped articular ends
• Dorsal rib - epipleural rib

  Ventral rib - pleural rib
• Ribs have spongy bones
• Ventral rib head

  Capitulum
• Capitulum

  • Reptiles & birds
  • capitulum articulates with pleurocentrum
  • Mammals
  • capitulum articulates between centra
• Animals without a sternum

  • Fishes
  • Turtles
  • Snakes
  • Limbless lizards
• Sternum

  • Fishes
  • sternum absent
  • Urodela (salamanders)
  • sternal plate - sternum is in a plate-like structure
  • Anura (frogs)
  • xiphisternum with xiphoid cartilage
  • omosternum with sternum cartilage
  • Turtles / snakes / limbless lizards
  • no sternum
  • ribs form a plate like shell
  • especially testudinata
  • Other reptiles
  • ex: lizards
  • sternum present
  • single midventral element
  • Birds
  • sternum with prominent carina
• Sternum - Mammals

  • Mammals
  • sternum is composed of sternebrae serial elements
  • Sternebrae - serial elements; chain of ossified elements
  • advantage: better breathing
  • reason why it is easier to crush rib cage during cpr
  • modifications in sterna
  • Manubrium - uppermost portion
  • Xiphisternum - lowermost portion
• Classification of caudal tail based on where vertebral column extends to which part

  • Heterocercal
  • upper lobe of fin
  • primitive fishes
  • Diphycercal
  • extends to tail but more medial & less extension
  • Homocercal
  • extends just below the tail
  • Hypocercal
  • vertebral column extends to opposite direction that homocercal condition
  • extends dorsally
  • more common in ostracoderms
• Regulates lateral movement of snakes


  Zygantrum
• Sides of shell

  • dorsal - carapace
  • ventral - plastron