CC

Axial Skeleton

What are the main components of the axial skeleton in vertebrates? Vertebral column, ribs, sternum (or keel in birds).

What are the functions of the vertebral column? Structural support (replaces notochord), muscle attachment, protection of spinal cord and blood vessels.

What are the different shapes of vertebral centra? What animals are they found in?

  • Acoelus: flat ends (most mammals)

  • Amphicoelus: concave both ends (fish, salamanders, caecilians)

  • Procoelus: concave cranial, convex caudal (modern reptiles, anurans)

  • Opisthocoelus: convex cranial, concave caudal (salamanders, some mammals)

  • Heterocoelus: saddle-shaped ends (birds, some turtles)

How does vertebral articulation affect the movement and the spinal cord? Articulation type determines flexibility and range of motion. More concave/convex shapes allow greater movement while protecting the spinal cord.

Which vertebral shape offers the highest movement capabilities? Heterocoelus vertebrae—found in bird necks—allow extensive movement.

What are the components and functions of intervertebral bodies in mammals?

  • Annulus fibrosis: outer fibrocartilage ring

  • Nucleus pulposus: inner gel-like core (notochord remnant) Function: shock absorption, flexibility, cushioning between vertebrae.

What is the sternum, and in which vertebrate groups is it absent? Ventral bone of rib cage. Absent in fish, turtles, snakes, and most amphibians (except anurans).

Describe the origin and components of the plastron in turtles. Is the plastron a sternum? No, the plastron is not a sternum. It originates from clavicles, interclavicle, and gastralia. It forms the ventral shell.

How is the sternum modified in birds, and what is its function? Birds have a keel (carina), a ventral extension of the sternum for flight muscle attachment.

What are sternebrae, the manubrium, and the xiphoid process? Sternebrae: segmented parts of the mammalian sternum. Manubrium: cranial-most segment. Xiphoid process: caudal-most segment.

What are the functions of ribs? Muscle attachment, protection of thoracic organs, and aiding respiration.

Describe the types and locations of ribs in fish. Fish have dorsal and ventral ribs. Trunk vertebrae bear ribs; caudal vertebrae do not.

How are bird ribs adapted for flight? What are uncinate processes and what are their functions? Bird ribs are flattened and fused to vertebrae. Uncinate processes are bony projections that reinforce the rib cage and aid in respiration.

Differentiate between true ribs, false ribs, and floating ribs.

  • True ribs: articulate directly with sternum

  • False ribs: connect indirectly or to each other

  • Floating ribs: no ventral articulation

What are the two parts of a rib? What is the name for the junction where they meet?

  • Vertebral rib (proximal)

  • Sternal rib (ventral, often cartilaginous) They meet at the costochondral junction.

Describe the tuberculum, capitulum, and facet in relation to ribs.

  • Tuberculum: dorsal part of vertebral rib

  • Capitulum: ventral head of vertebral rib

  • Facet: articulation point on vertebra for rib attachment

How are ribs and vertebrae modified in turtles? Thoracic vertebrae and ribs are fused with the carapace. C8 is fused; cervical vertebrae are heterocoelus.

Describe the vertebral differentiation and rib structure in snakes. What are zygopophyses, and what is their function in snakes? Snakes have trunk vertebrae with ribs and caudal vertebrae without ribs. Zygopophyses (zygosphene and zygantrum) interlock to prevent twisting.

Describe the specialized vertebral structures in anurans (frogs). Short neck (only atlas), limited head movement, and a fused caudal vertebra called the urostyle.

What are the regions of the vertebral column in reptiles like crocodiles and lizards? Cervical, thoracic, lumbar, sacral, caudal. May also have gastralia (dermal bones in ventral abdomen).

What are gastralia and who has them? Dermal bones in the ventral abdomen. Found in reptiles like crocodiles; support abdominal muscles.

What are the different regions of the vertebral column in birds? Name and describe the fused sections of vertebrae.

  • Cervical: atlas/axis, heterocoelus

  • Thoracic: fused

  • Synsacrum: fusion of thoracic, lumbar, sacral, and some caudal vertebrae

  • Caudal: ends in pygostyle

Describe the structure and function of the pygostyle in birds. Fused terminal caudal vertebrae. Supports tail feathers and aids in flight maneuvering.

Name the five regions of the vertebral column in mammals and be able to label them. Cervical (7), thoracic, lumbar, sacral (3–5 fused into sacrum), caudal.

How are vertebrae named and junctions labeled? Named by region and position (e.g., C1 = atlas, T1 = first thoracic). Junctions labeled by adjacent vertebrae (e.g., C7-T1).

Describe the structure and function of the atlas and axis. Atlas (C1): supports skull, allows nodding. Axis (C2): has odontoid process (dens), allows rotation.

How many sacral vertebrae are typically found in mammals, and what structure do they form? Typically 3–5 sacral vertebrae, fused to form the sacrum.

What is the synsacrum and which animals have it? A fused structure in birds combining thoracic, lumbar, sacral, and caudal vertebrae. Provides rigidity for flight.

What is the urostyle and which animals have it? A fused caudal vertebra in anurans (frogs). Aids in jumping and shock absorption.

What are hemal spines and where are they found? Ventral projections on caudal vertebrae in fish. Protect blood vessels.

What is skeletal deregionalization and where is it seen? Loss of distinct vertebral regions. Seen in snakes, which have many similar trunk vertebrae.