Chapter 7: Cranial Skeleton Flashcards
Embryology of chondrocranium
Notochord (landmark) Occipital arch Parachordal cartilage [para=around] Trabeculae Sense capsules -otic (ear) -optic (eye) -olfactory (nasal)
Chondrocranium
"neurocranium" Always present Cartilage or bone Primitive brain case Sense capsules Ex: occipital and ethmoid Protects brain -shark is atypical = totally cartilage
What vertebrates have non-ossified chondrocranium?
Agnathas
Early placoderms
Chondrichthyes
Trend of ossification
Bony fish (portions of ossification)
Mammals (entirely)
Cartilage–>bony
Splanchnocranium
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
Early splanchnocranium
Pharyngeal bars -generalized
- feeding (strain H2O through)
- gas exchange
Tetrapod splanchnocranium
Gills no longer for gas exchange
-remodel skeleton + muscles
EX: tongue support, vocal apparatus
Splanchnocranium gill slits
Early vertebrates: up to 15
Jawed vertebrates: 5 or 6
Splanch: branchial arch 3-7
Basic arch skeletal elements (dorsal->ventral) 5 arches, support gills 1) pharynobranchial 2) epibranchial 3) ceratobranchial 4) hypobranchial 5) basibranchial
Arch 1
Mandibular arch
2 components:
Palatoquadrate = upper jaw
Mandibular (Meckel’s) cartilage = lower jaw
Arch 2
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
Types of jaw support
Hyostylic
Amphistylic
Autostylic
Hyostylic support
Support by hyomandibula (of arch 2) only
Sharks
Amphistylic support
Support by hyomandibula AND direct connection to braincase via a ligament to orbital process
Sharks and bony fish
Autostylic support
NO support by hyomandibula, only a direct connection to skull placoderms; modern tetrapods
Dermatocranium
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
Comparative skulls: Agnatha
Ostracoderms:
Chondrocranium of cartilage
Dermatocranium (shell-skin)
Splanchnocranium -all arches are branchial
Cyclostomes:
Chondrocranium of cartilage
No dermatocranium
Splanchnocranium -all arches are branchial
Comparative skulls: placoderms
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
Comparative skulls: Chondrichthyes
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
Comparative skulls: Osteichthyes
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
Comparative skulls: amphibians
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
Comparative skulls: reptiles and birds
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
Temporal fenestra
Hole in dermal roofing bones
Advantages:
Lighter skull
Room for more muscles > greater bite force
Muscle flexion
Remnants in mammals: sagittal crest & zygomatic arch
Comparative skulls: mammals
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
Mammal ear ossicles
- distinguishing characteristic *
- incus
- malleus
- stapes
(Be able to trace the evolutionary precursors of these bones throughout our phylogeny - fig 7.55)
