Outline-1, BIO 3220, Axial Skeleton, Skull


A. Introduction and history

Cephalization –Need cranium to house brain & sensory structures

B. NEUROCRANIUM –Primarily floors and walls of cranium

1. Function –Protect

2. Phylogeny –All vertebrates have this; Replacement bone

3. Development of chondrocranium

a. Prechordal cartilage = trabeculae cranii

1. Forebrain

2. Nasal capsules

3. Orbits

4. Rostrum

5. Ethmoid plate

b. Parachordal cartilage –Beside and behind notochord

1. Hindbrain

2. Basal plate

3. 1-2 Occipital condyles and foramen magnum

4. Sense capsules

a. Olfactory capsules

b. Otic capsule

c. Optic capsule

5. Ethmoid plate & Basal plate Expansion –Ethmoid plate unites with olfactory capsules; basal plate unites with otic capsule

a. Foramina

b. Hypophyseal fenestra (In basal plate)

6. Ossification Centers –SEE Skull & Lower Jaw Components Page

a. Occipital

1. Foramen Magnum

2. Basioccipital

3. Exoccipital

4. Supraoccipital

5. Occipital Condyles

b. Otic

c. Sphenoid

1. Basisphenoid

2. Presphenoid/Sphenethmoid

d. Ethmoid

1. Ethmoid plate

2. Olfactory capsules


1. Phylogeny –Membrane bone which evolved from dermal armor

2. Roofing bones –SEE Skull & Lower Jaw Components Page

a. Nasal

b. Frontal

c. Parietal

d. Orbit

1. Lacrimal

2. Jugal = Infraorbital = Zygomatic

e. Squamosal

3. Upper and Lower jaw

a. Premaxilla

b. Maxilla

c. Dentary

d. Splenial

e. Surangular

f. Angular

g. Coronoid

h. Prearticular

4. Primary palatal bones

a. Definition

b. Vomer

c. Palatine

d. Pterygoid

5. Opercular bones

D. SPLANCHNOCRANIUM = visceral skeleton


1. Function –Supports and allows movement of jaws, gills, tongue, associated with hearing

2. Evolution –Ancient; Replacement bone

3. Gill Slits(typically 6)

4. Visceral arch

a. Pharyngobranchial

b. Epibranchial

c. Ceratobranchial

d. Hypobranchial

e. +/- Basibranchial

5. Mandibular arch

a. Palatoquadrate

b. Mandibular = Meckel’s Cartilage

6. Hyoid arch

a. Hyomandibula

b. Ceratohyal

c. Basihyal

E. Interrelationships


1. Chondrocranium

-protects brain, otic, and nasal organs

2. Visceral skeleton continuous –Pharyngeal basket, branchial in function

3. Dermal skeleton –None to armor, depending on group


1. Chondrocranium

2. Splanchnocranium

a. Jaws from first visceral arch

b. Autostylic suspension

3. Dermal armor


1. Chondrocranium

a. Calcification

b. 2 Occipital condyles, foramen magnum

c. Otic and nasal capsule –Fused to neurocranium

2. No dermal bones

3. Splanchnocranium –SEE Visceral Arches Page

a. Mandibular arch

b. Hyoid arch

c. Amphistylic –Primitive sharks, some modern ones

d. Hyostylic –Most sharks; Hyomandibula hangs from otic capsule

e. Autostylic –Chimeras


1. Neurocranium

a. Incomplete above brain

b. Chondrostean

cartilaginous in most

c. Holosteans


d. Teleosts

1. Large # bones

2. Ossification centers of walls/floor




occipital {1 condyle}

e. Dipnoans – cartilaginous

2. Dermatocranium

a. Complete –Joins to pectoral girdle

b. Support teeth –Maxilla, Premaxilla

c. Numerous; overlying neurocranium

d. Similar amongst orders except broad plates in dipnoans

e. Moveable bony operculum

3. Splanchnocranium –SEE Visceral Arches Page

a. Bone replacement(except dipnoans)

b. Quadrate –Replacement of palatoquadrate

c. Articular

d. Hyomandibular + more segments; Arch II is not branchial in function

e. 5 branchial arches [3-7]

f. Hyostylic –Highly moveable; Ray-finned fish

g. Amphistylic –Crossopterygians

h. Autostylic –Dipnoans


1. Neurocranium & Dermatocranium –SEE Skull & Lower Jaw Components Page

a. Neurocranium is incomplete dorsally, more cartilage than in bony fish; flat

b. Not joined to pectoral girdle

c. 2 Occipital condyles

2. Splanchnocranium –SEE Visceral Arches Page

a. Larval stages

b. Quadrate – autostylic

c. Epipterygoid absent

d. Articular [unchanged]

e. Columella [= stapes]

f. Hyoid apparatus –Tongue support

g. Larynx –New


1. Neurocranium

a. Decreased # bones

b. 1 occipital condyle [except therapsids]

c. Well ossified

2. Dermatocranium –SEE Skull & Lower Jaw Components Page

a. Full complement – some reduction in roof bones

b. Temporal region

1. Temporal fossa or fenestra

a. Infratemporal arch –Below ventral fossa

b. Zygomatic arch

c. Supratemporal arch –Below dorsal fossa

2. Anapsid– Turtle; Stem reptiles

3. Synapsids– Mammal-like

4. Diapsids– Lizards, Crocodiles (May have modifications)

5. Euryapsids– Extinct reptiles such as Pleisosaurs and Ichthyosaurs, with one dorsal fossa

6. Eating –Allows rotary chewing

c. Secondary Palate

1. Palatine process of the Maxilla

2. Palatines

3. Internal nares shift posteriorly

4. Purpose –Allows simultaneous chewing & breathing

d. Cranial kinesis– Independent movement of one or more skull bones, such as pivoting quadrates

3. Splanchnocranium

a. Quadrate {Autostylic suspension}

b. Articular

c.Stapes –Homologous to hyomandibula

d. Hyoid apparatus –Arch II (some 3-4)

e. Larynx –Arch V

4. Changes in Therapsids

a. Neurocranium

-2 occipital condyles

b. Dermatocranium – Synapsid

c. Splanchnocranium

1. Quadrate & Articular freed

2. Squamosal & Dentary articulate


1. Neurocranium

a. Larger, highly vaulted, modified reptile skull

b. Incomplete dorsally

c. Well ossified & fused

d. 1 occipital condyle

2. Dermatocranium

a. Modified diapsid –Supratemporal arch is lost, so one big opening confluent with orbit

b. Premaxilla and dentary = bony parts of beak

c. Cranial kinesis –Quadrate & Upper jaw

3. Splanchnocranium

-Similar to reptiles


1. Neurocranium

a. Larger

b. Fusions & Loss of bones –SEE Skull & Lower Jaw Components Page

c. Sutures

d. Fontanels

e. Sinuses

f. 2 occipital condyles

2. Dermatocranium

a. Nasal structures

Conchae = turbinates (from neurocranium too)

b. Tympanic bulla –New, unique, encloses middle ear

c. Malleus

1. Prearticular

2. Articular (splanchnocranium)

d. Squamosal articulation with dentary bone [sole lower jaw bone]

e. Synapsid

f. Decreased # bones

3. Splanchnocranium –SEE Visceral Arches Page

a. Quadrate – incus

b. Articular – malleus


1. Decreased # bones/ossification centers

2. Decreased # visceral arches early

3. Homology

-Hyomandibula & stapes

4. Analogy

-Quadrate/articular joint

-Squamosal/dentary joint

5. Preadaptation –Columella, as amphibian ear is rudimentary