Chapter 7: Cranial Skeleton

Question 0

Embryology of chondrocranium

Answer 0

Notochord (landmark)
Occipital arch
Parachordal cartilage  
   [para=around]
Trabeculae
Sense capsules 
  -otic (ear)
  -optic (eye)
  -olfactory (nasal)

Question 1

Chondrocranium

Answer 1

"neurocranium"
Always present
Cartilage or bone
Primitive brain case
Sense capsules
Ex: occipital and ethmoid 
Protects brain 
-shark is atypical = totally cartilage

Question 2

What vertebrates have non-ossified chondrocranium?

Answer 2

Agnathas
Early placoderms
Chondrichthyes

Question 3

Trend of ossification

Answer 3

Bony fish (portions of ossification)
Mammals (entirely)
Cartilage–>bony

Question 4

Splanchnocranium

Answer 4

Always present
Cartilage or bone
Embryology: primitive pharyngeal arches
Ex: gills, jaws, jaw support, ear ossicles, larynx
Palatoquadrate cartilage + replacement bone
Mandibular (Meckel’s) cartilage + replacement bone
Skeleton of branchial arches

Question 5

Early splanchnocranium

Answer 5

Pharyngeal bars -generalized

• feeding (strain H2O through)
• gas exchange

Question 6

Tetrapod splanchnocranium

Answer 6

Gills no longer for gas exchange
-remodel skeleton + muscles
EX: tongue support, vocal apparatus

Question 7

Splanchnocranium gill slits

Answer 7

Early vertebrates: up to 15

Jawed vertebrates: 5 or 6

Question 8

Splanch: branchial arch 3-7

Answer 8

Basic arch skeletal elements (dorsal->ventral)
5 arches, support gills
1) pharynobranchial
2) epibranchial
3) ceratobranchial
4) hypobranchial
5) basibranchial

Question 9

Arch 1

Answer 9

Mandibular arch
2 components:
Palatoquadrate = upper jaw
Mandibular (Meckel’s) cartilage = lower jaw

Question 10

Arch 2

Answer 10

Hyoid arch (pushed against mandibular arch)
Basic arch elements:
1) hyomandibula
2) ceratohyal
3) basihyal
*hyomandibula only part incorporated into skull as jaw support
*ceratohyal for tongue support
*formation of hyoid not associated w/ formation of jaws
*placoderms had jaw but arch 2 remained branchial > gill tissue

Question 11

Types of jaw support

Answer 11

Hyostylic
Amphistylic
Autostylic

Question 12

Hyostylic support

Answer 12

Support by hyomandibula (of arch 2) only

Sharks

Question 13

Amphistylic support

Answer 13

Support by hyomandibula AND direct connection to braincase via a ligament to orbital process
Sharks and bony fish

Question 14

Autostylic support

Answer 14

NO support by hyomandibula, only a direct connection to skull placoderms; modern tetrapods

Question 15

Dermatocranium

Answer 15

Solid plates covering the chondrocranium and brain
Early fish have heavy dermal armor trend toward reduction
Major reduction in dermal roofing bones in mammals
Cyclostomes and Chondrichthyes lack dermatocranium

Question 16

Comparative skulls: Agnatha

Answer 16

Ostracoderms:
Chondrocranium of cartilage
Dermatocranium (shell-skin)
Splanchnocranium -all arches are branchial

Cyclostomes:
Chondrocranium of cartilage
No dermatocranium
Splanchnocranium -all arches are branchial

Question 17

Comparative skulls: placoderms

Answer 17

Chondro- cartilaginous, becoming partly ossified
Dermato- heavy dermal armor, large plates
Splanch- arch 1: jaws, autostylic support (NOT hinge; attachment to skull)
Arch 2-7 are branchial

Question 18

Comparative skulls: Chondrichthyes

Answer 18

Chondro- cartilaginous = specialized 
Dermato- lost, no dermal bone
Splanch- arch 1 = jaws
Arch 2 = jaw support (no longer branchial) hyostylic or amphistylic
Arch 3-7 are branchial

Question 19

Comparative skulls: Osteichthyes

Answer 19

Chondro- well ossified
Dermato- dermal bone covers cartilage; locks them in skull attachment to pectoral girdle
Splanch- arch 1 = jaws; hinge b/w quad rate and articular
Arch 2 = jaw support (parallel to shark evolution) hyostylic or amphistylic
Arch 3-7 branchial

Question 20

Comparative skulls: amphibians

Answer 20

Chondro- yes
Dermato- loss of operculum; reduction of bones
Splanch- arch 1 = jaw, hinge quadrate and articular. Jaw support =. Autostylic only
Arch 2 = hyomandibula > columella (ear ossicle)
Rest of arch 2 = hyoid> tongue support
Arch 3-7 remodeled for larynx and sound production

Question 21

Comparative skulls: reptiles and birds

Answer 21

Chondro- yes
Dermato- 3 options> anapsid, diapsid, synapsid
Splanch- (similar to amphibians) 
Arch 1 = jaw, hinge quadrate, articular
Jaw support = autostylic only
Arch 2 = hyomandibula > columella (ear ossicle) 
Rest of arch 2 = hyoid > tongue support
Arch 3-7 = larynx

Question 22

Temporal fenestra

Answer 22

Hole in dermal roofing bones

Advantages:
Lighter skull
Room for more muscles > greater bite force
Muscle flexion

Remnants in mammals: sagittal crest & zygomatic arch

Question 23

Comparative skulls: mammals

Answer 23

Chondro- yes> reduced: ethmoid & occipital
Dermato- large temporal fenestra, weight reduction. Secondary palate complete- why important? Increase oxygen to eat and breath at the same time, especially in endotherms.
Splanch- arch 1- jaws; hinge is temporal (squamosal) and dentary
*quadrate from arch 1 = incus
*articular from arch 1 = malleus
Arch 2- columella > now stapes
Arch 3-7 are larynx, trachea

Question 24

Mammal ear ossicles

Answer 24

• distinguishing characteristic *
• incus
• malleus
• stapes

(Be able to trace the evolutionary precursors of these bones throughout our phylogeny - fig 7.55)