Vertebrate Head Skeleton

Question 1

skull

Answer 1

brain case
upper jaw
lower jaw

Question 2

head skeleton

Answer 2

neurocranium
dermatocranium
splanchnocranium

Question 3

Neurocranium

Answer 3

= entire braincase in Chondrichthyes; chondrocranium

lesser contribution of neurocranium in other Gnathostomes:
focus on tetrapods
4 ossification centers

bones derived from neurocranium are ENDOCHONDRAL

Question 4

ossification centers of neurocranium

Answer 4

occipital center
sphenoid center
ethmoid center
otic center

Question 5

occipital center of ossification of neurocranium

Answer 5

location: posterior floor of brain

surrounds foramen magnum; yields up to 4 bones: supraoccipital, exoccipital (2), basioccipital –> ankylose

occipital condyles: from various occipital bones

“fish” and reptiles: one condyle (basioccipital with some contribution of exoccipital)

Enlarged exoccipitals (reduced contributions of other occipital bones): 2 condyles – mammals

Question 6

sphenoid center of ossification of neurocranium

Answer 6

location: central and lateral floor

basisphenoid, presphenoid

sella turcica = upper region of basisphenoid

Alisphenoid (greater wing) in mammals forms from the upper jaw cartilage and fuses with other sphenoid bones (thus a composite bone)

Question 7

ethmoid center of ossification of neurocranium

Answer 7

location: anterior and medial floor

turbinate cartilages (turbinate conchae/nasal conchae) in amniotes

nasal conchae may/may not ossify

cribriform plate and crista galli: ethmoid

Question 8

otic center of ossification of neurocranium

Answer 8

cartilaginous otic capsule (encloses inner ear organs)

“otic bones”: prootic, opisthotic, epiotic (one on each side)

in tetrapods: otic bones fuse - form petrosal bone

mammals: petrosal unites with squamosal bone (membrane bone) to form temporal bone

Note: temporal bone = composite bone = contribution from different ossification centers

Question 9

Dermatocranium

Answer 9

all membrane bone, no endochondral contribution

forms:

• side and roof of cranium enclosing brain
• “palate” bones
• upper jaw bones
• lower jaw bones

Question 10

Dermatocranium series

Answer 10

vault series
orbital series
temporal series
palatal series
facial series
mandibular series

Question 11

Vault series of the dermatocranium

Answer 11

“roofing bones”

most are paired: frontal, parietal, post-parietal (=interparietal when fused) – occasionally present in humans

seen as “extra bone” in humans = Wormian bone

Question 12

Orbital series of the dermatocranium

Answer 12

circumorbital bones

define eye orbit

lacrimal, prefrontal, postfrontal, postorbital, jugal

Question 13

Temporal series of the dermatocranium

Answer 13

behind orbit; posterolateral wall of braincase)

temporal fenestrae associated with temporal series (and jugal of orbital series)

fenestrae function???

lateral position: squamosal and quadratojugal (contribute to cheek)

medial position: supratemporal, intertemporal, tabular

Question 14

Primary palate bones of the dermatocranium

Answer 14

applied to ventral floor of neurocranium

vomer, palatine, pterygoid, ectopterygoid, parasphenoid

teeth usually present on primary palate bones in teleosts, amphibians, non-avian reptiles

Note: primary palate is not the hard palate!

primary palate = bony roof of buccal cavity in amphibians = bony roof nasal passage in amniotes

hard palate in amniotes = bony roof of mouth; hard palate = secondary palate

Question 15

facial series of the dermatocranium

Answer 15

mostly membrane bones of upper jaw

premaxilla, maxilla, nasal

form in dermis and fuse with primary palate in T thus upper jaw = part of the skull in tetrapods

premaxilla and maxilla bear teeth

Question 16

palatoquadrate cartilage

Answer 16

upper jaw in Chondrichthyes

not homologous to maxilla

forms:

• alisphenoid
• quadrate bone (posterior region of upper jaw)

Question 17

mandibular series of the dermatocranium

Answer 17

membrane bones of lower jaw

lateral: dentary, splenial, angular, surangular
medial: coronoid, prearticular

Question 18

Splanchnocranium

Answer 18

“visceral cranium”

skeleton of pharyngeal arches incorporated into head skeleton

=embryonic upper jaw cartilage (palatoquadrate) and its replacement bone

embryonic lower jaw cartilage (Meckel’s cartilage) and its replacements bone

Question 19

Meckel’s cartilage

Answer 19

lower jaw cartilage

forms:
-articular bone (posterior region of lower jaw)

Question 20

articulation of jaw

Answer 20

quadrate and articular represent articulation of jaw in tetrapods

mammal articulation: squamosal (mandibular fossa) and dentary (mandibular condyle)

Question 21

quadrate bone

Answer 21

derived from palatoquadrate cartilage

in amphibians and reptiles: articulates with articular bone in lower jaw

in mammals: becomes incus = anvil (middle ear)

i.e. incus is homologous to lower jaw in amphibians/reptiles

amphibians/reptiles have 1 middle ear bone, mammals have 3

Question 22

articular bone

Answer 22

from Meckel’s cartilage

in amphibians and reptiles: articulates with quadrate in upper jaw

in mammals: becomes malleus = hammer (middle ear)

i.e. malleus is homologous to upper jaw in amphibians/reptiles

amphibians/reptiles have 1 middle ear bone, mammals have 3