Cranial vs. Postcranial

Composite Structure (3):

1. Chondrocranium

2. Dermatocranium

3. Splancho Cranium

Brian Case.

Compose of fused components immediately surrounding and supporting the brain.

Underlies and supports the brain.

Lies in series with bases of vertebrae.

Formed from neural crest cells and mesenchyme.

In most vert, this is primarily embryonic as a scaffold for development of brain and support for sensory structures.

• Composed of dermal bones.
• Formed in the dermis and sinks inward to be applied to chondro and splancho.
• Forms the sides and roof of the skull, bony lining of mouth and encases splancho.
• Teeth rest on dermal bone.
• Absent in chondrichthyes.
• Predominates in amniotes forming most of the brain case and lower jaw.

• Oldest
• Arose to support pharyngeal slits.
• In fish this supports gills and is a site of resp muscle attachment.
• In gnathostomes, it conributes to the jaw and hyoid apparatus.
• In mammals, this contributes hyoid apparatus and forms 3 bones in the middle ear and a styloid process.
• Forms from the neural crest that migrate to the pharynx between phary slits that diff into pharyngeal arches.

Each arch is a series of 5 elements.

Jaws are branchial arches that support the mouth.

1st: 2 arches, names first mandibular arch.

2nd: Hyoid arch

There are 7 arches (2 are jaws, then brachial I-V)

Said to arise from the anterior gill arches.

Evidence:

1. Jaws and branchial arches devp similarly and in series and both are from neural crest in sharks.
2. Similar distribution of blood vessels and nerves in jaws and branchial arches
3. Jaw muscles are modified arch musculature.

1. Jaws are a major evolutionary event.

2. Jaws reflect a more active lifestyle and diet shift.

3. Splancho contribution decreases in mammals.

Lack strong, direct skull attachment.

Suspended at two sides.

Protrusible jaw.

Opens jaws, mandible lowered, jaws move forward.

Upper jaw freely articulates with the skull.

Increase mobility due to change and loss of bones.

No cross connection between L/R sides.

Both sides join at mandibular symphasis (indep movement)

"walk" over prey to swallow.

Can flare jaws.

• Changes to lower jaw; lower = dentary.
• 3 middle ear bones (splanchno)
• Change in the way that food is prepared before swallowed (mastication).
• 2' palate.
• Precise tooth occlusion.
• Specialized teeth.
• Diphydont teeth.
• Akinetic Skull (firm)