VERTEBRATE SKULLS

Report
Mrs. Ofelia Solano Saludar
Department of Natural Sciences
University of St. La Salle
Bacolod City
The vertebrate
skull consists of:
Neurocranium (also called
endocranium, chondrocranium or primary
braincase)
Dermatocranium (membrane or dermal
bones)
Splanchnocranium (visceral skeleton)


Cartilaginous stage protects the brain
Begins as a pair of parachordal cartilages
alongside the notochord (derived from sclerotome),
and the prechordal cartilages or trabeculae cranii
(derived from neural crests) anterior to these.
Cartilages derived from neural crest also
appears in the:
1. olfactory capsules partially surrounding the
nasal epithelium,
2. otic capsule surrounding the inner ear,
3. orbital/ optic capsules around the eyes
Completion of floor, walls, & roof:

Parachordals join the notochord and expand to
form the basal plate, floor of hindbrain, occipital
condyles (1-2), and foramen magnum

Ethmoid plate – prechordals fuse with olfactory
capsules; optic capsules remain independent
 Basal plate - fuses with otic capsules
 Development of cartilaginous walls (sides of
braincase) and a cartilaginous roof over the
brain in cartilaginous fishes
 Foramina remain for nerves & blood vessels
 Hypophyseal fenestra remains for pituitary
gland and carotid arteries
Cartilaginous fishes - retain a cartilaginous
neurocranium throughout life; completes
skull by forming a cartilaginous roof
(tectum) over neurocranium
Bony fishes, lungfishes,
& most ganoids - retain
highly cartilaginous
neurocranium that is
covered by membrane
bone
Cyclostomes- the
cartilaginous
components of the
embryonic
neurocranium remain
in adults as
independent cartilages
Reptiles: Embryonic Development of Lizard
Chondrocranium: Parachordal and trabecular
cartilages grow up around brain and sense organs
 Consists of membrane bones that
encase the chondrocranium and jaws.
 Formed a complete roof for the skull
of extinct tetrapods, but became
reduced in number through loss.
 Vacuities also tend to arise in the
posterior part of the roof, and these
temporal fossae are of importance in
the evolution of the various amniotes.
Temporal fossae
(plus mammalian
zygomatic arch)
provide space
and surfaces in
advantageous
positions for
accommodating
the large
powerful muscles
(adductor,
masseter,
temporalis) that
operate the lower
jaw of amniotes.
Differentiation of
synapsid adductor
mandibulae into
temporalis,
superficial
masseter, and
deep masseter,
opposed along the
jaw by the
pterygoideus
The dermatocranium
lies superficial to the
neurocranium & forms
the bones of:
 Roof of the brain:
nasals, frontals,
parietals, postparietals
 Posterior angle of
skull: intertemporal,
supratemporal,
tabular, squamosal, quadratojugal
 Around orbits: lacrimal, prefrontal, postfrontal,
jugal (infraorbital), postorbital
 The upper jaw: premaxilla, maxilla
 The lower jaw: splenial, postsplenial, angular
(tympanic bulla), surangular, prearticular
(anterior malleus in mammals), coronoids,
dentary
 The palate: parasphenoids, vomer
palatines,
pterygoids,
ectopterygoids
(cover palatoquadrate)
 The operculum in
fishes
PALATAL BONES – the primary
palate is the floor on which the
brain rests, & the roof of the oral
cavity in fishes & amphibians;
remain cartilaginous in sharks.
 Birds, mammals, some reptiles:
 A secondary palate (plus a soft
palate in mammals) develops
from processes of the
premaxillae, maxillae, and
palatines, creating a horizontal
partition that separates the oral
cavity into nasal & oral passages
 Allows chewing and breathing
simultaneously
 Parasphenoid is lost and internal
nares is displaced caudad when
palate forms
Evolution of the mammalian bony palate:
dermal bones of the margin of the oral cavity
expand medially to house nasal passages from
external nares to choanae.
 Cartilage blastema origin is neural crest
 Consists of typically 7 gill or skeletal visceral/
branchial arches
1st MANDIBULAR ARCH
 Dorsal half forms the
primitive upper jaw,
the palatoquadrate
or pterygoquadrate
 Lower half forms the
lower jaw, the Meckel’s cartilage
 The upper jaw becomes incorporated into the
skull, while the lower jaw forms a movable joint
with it.
1. PALATOQUADRATE CARTILAGES:
 Unossified in tetrapods, function is taken
over by dermal bones
 Ossifications occur only in the ascending
process (epipterygoid bone), and in the otic
process (quadrate bone) which becomes an
immovable part of auditory region (except in
streptostylic conditions which permits wide
gape for swallowing large prey)
2. MECKEL’S CARTILAGES:
 Anterior mentomeckelian bone of
amphibians
 At the rear is the articular bone which
articulates with the quadrate bone of the
upper jaw (autostylic suspension)
2nd HYOID ARCH and other gill arches:
 Composed of dorsal paired hyomandibular
cartilages, and lateral gill-bearing ceratohyals
of elasmobranchs.
 The remainder and the other 5 arches contribute
to the hyoid apparatus and laryngeal cartilages
of tetrapods.
 Operculum is the
fold of the hyoid
arch that extends
over the gill slits
in holocephalans
& bony fishes; in
tetrapods no
vestiges of opercular bones remain
HYOID CARTILAGES
Hyomandibular cartilage ossifies to form
hyomandibula of fishes and suspend lower jaw
(hyostylic suspension); in tetrapods, it gives
rise partly to the columella of the ear
Remainder of hyoid arch fuse with gill arches to
form hyobranchial skeleton consisting of:
 Hyoid apparatus - serves as support for
tongue and larynx, muscle attachment,
buccal respiration of amphibians
 Laryngeal cartilages- support voice box
chamber
CENTERS OF OSSIFICATION appear which
converts the chondrocranium into a complete
skull that consists of:
 Cartilage bones ossified in the
chondrocranium, sense capsules, hyoid and
mandibular arches
 Dermal bones covering the cartilage bones
everywhere except on midventral surface and
posterior end of the skull.
Degree of ossification is greater in higher
members of each group; cartilaginous skulls
result from retrogressive processes.
OCCIPITAL CENTERS
Occipital group:
encircling the
foramen magnum are
the: basioccipital,
exoccipital (2),
supraoccipital
In mammals, all 4
occipital elements
typically fuse to form
a single occipital
bone surrounding the
foramen magnum
 Occipital condyles are projections by which
the skull articulates with the atlas.
 Fishes and
primitive tetrapods have only 1
condyle formed
by basioccipital
and partly by
exoccipital.
 2 condyles
present in
amphibians and
mammals result from reduction of
basioccipital and enlargement of exoccipital.
 Posterior sphenoid group: basisphenoid,
pleurosphenoid (not the mammalian alisphenoid,
epipterygoid location)
 Orbitosphenethmoid region: presphenoid,
orbitosphenoids, mesethmoid.
 In mammals, the
basicranial axis
is occupied by:
basioccipital,
basisphenoid,
presphenoid,
mesethmoid
(absent in some)
 Remain cartilaginous & form anterior to sphenoid
 In most mammals, the nasal chamber is large & filled
with ridges from the ethmoid bones called the
turbinals or ethmoturbinals.
 These bones are covered with olfactory epithelium
in life and serve to increase the surface area for a
more acute sense of
smell (olfaction).
 Another ethmoid
bone, the cribriform
plate, separates the
nasal chamber from
the brain cavity
within the skull.
SENSE CAPSULES:
1. OTIC - the cartilaginous otic capsule is replaced
in lower vertebrates by several bones: prootic,
opisthotic, epiotic, pterotic, sphenotic
•
One or more of these may unite with adjacent
replacement or membrane bones:
Frogs & most reptiles - opisthotics fuse with
exoccipitals
 Birds & mammals - prootic, opisthotic, &
epiotic unite to form a single petrosal (periotic
or petromastoid) bone; the petrosal, in turn,
sometimes fuses with the squamosal to form
the temporal bone
2. OPTIC – gives rise to sclerotic bones around pupil
of reptiles and birds (absent in mammals)

blue- chondrocranium; pink-dermatocranium;
yellow- splanchnocranium
JAW SUSPENSIONS
 Autostyly (left) - hyomandibula has no role in
bracing the jaws (lungfish & tetrapods)
 Amphistyly (middle) - jaws & hyomandibula both
braced directly against the braincase (extinct
sharks)
 Hyostyly (right) - mandibular cartilage is braced
against the otic capsule; jaws braced against
hyomandibula (sharks & present day bony fishes)
P
L
A
C
O
D
E
R
M
S
CROSSOPTERYGIANS- the dermatocranium forms
a series of paired and unpaired bones along middorsal line of skull
LABYRINTHODONTS- these unpaired bones are
lost but a series of paired bones resulted (nasals,
frontals, parietals, & dermoccipitals)
AGNATHA
 Chondrocranium:
remains cartilaginous
throughout life; skull
roof is fibrous and
protects brain &
sensory structures
 Splanchnocranium: no
ancestral branchial
skeleton; lingual
cartilage bears horny
teeth; continuous
basket with branchial
function
 Dermatocranium: no
dermal armor
CHONDRICTHYES
Chondrocranium: calcified; with 2 occipital
condyles and foramen magnum; otic and
nasal capsules fused to neurocranium
Splanchnocranium: mandibular arch gives
rise to palatoquadrate and Meckel’s
cartilages; hyoid arch composed of
hyomandibula, ceratohyal, basihyal cartilages
TELEOSTS
 Neurocranium: remain cartilaginous in
chondrosteans, neopterygians, dipnoans;
ossifies via the four ossification centers in
most fishes
 Dermatocranium: numerous dermal
bones overlying neurocranium
 Splanchnocranium: resembles that of
sharks except that bone is added;
anterior part of palatoquadrate
ensheathed by dermal maxilla and
premaxilla bones
 Caudal ends undergo endochondral ossification &
become the quadrate bone; the remainder becomes
the palatine & pterygoid bones.
 Caudal part of Meckel’s cartilage ossifies as articular
bones; remainder becomes invested by dentary and
angular membrane bones
 Hyomandibula ossifies to become symplectic and
interhyal bones
 Moveable bony
operculum
 Hyostylic
suspension
(ray-finned fish);
Autostylic
suspension
(Dipnoans);
Amphistylic suspension (Crossopterygians)
AMPHIBIANS
Neurocranium: remains cartilaginous except for
sphenethmoid, prootics, exoccipitals
 Dermatocranium
incomplete (lacrimals
and prefrontals only)
o lacks temporal region
o 2 occipital condyles
 Splanchnocranium: larval
stages have fish-like gills
supported by gill arches
o forms altered primary
palate with large
vacuities to allow
retraction of eyeballs

 Jaw suspension:
Quadrate of upper
jaw articulates with
articular of lower jaw
(autostylic
suspension)
 Hyomandibula is no
longer needed since
the jaw has an
autostylic suspension
 It is freed up and
becomes a
rudimentary stapes
called the columella
 The rest of the
hyoid arch plus
arches III and IV
become the
hyoid apparatus
for tongue
support
 Visceral arch V
is no longer
needed and
becomes the
new larynx;
arches VI and
VII are absent
REPTILES
Neurocranium:
 Well ossified, with
fewer bones, and
single occipital
condyle
Dermatocranium:
 Many bones, but fewer
than bony fish;
crocodilians retain the
largest number
 In many lizards, a
parietal foramen
houses a median eye
Splanchnocranium:






Similar to amphibians; snakes
have vestigial branchial skeleton
Stapes – functional columella
Hyoid apparatus: larynx
Quadrate-articular joint forms
autostylic suspension; forms
part of the kinetic mechanism of the skull
The hyoid consists of a body and 2 or 3 horns
(cornua) in the pharyngeal walls.
The entoglossus, a long bony
process extends from the hyoid
body forward into a long darting
tongue (snakes, lizards, birds).
EARLY TETRAPOD
SKULL
top: dermatochranium
removed
red: dermatocranium;
blue: chondrocranium;
green: splanchnocranium


Formation of partial or complete secondary palate
Development of temporal fossae bounded by
arches: infratemporal arch (below ventral fossa);
zygomatic arch (infratemporal arch); supratemporal
arch (below dorsal fossa)
CRANIAL KINESIS
Independent movement of one or more skull bones,
especially between the upper jaw and braincase;
e.g., a pivoting quadrate
 Results from reduction or loss
of arches along with presence
of intracranial joints
 Advantages:
o provides a way to change
the size and configuration
of the mouth rapidly
o optimize biting and rapid
feeding
 Disadvantages: lose force,
hard to optimize apposition
of occlusive surfaces

These
fossae and
arches
provide
room for
huge
chewing
muscles
which
allows rotary
chewing
BIRDS
 Neurocranium- thin,
highly vaulted or
domed, but basically
a reptile skull
 Dermatocranium:
Modified diapsid: supratemporal arch is lost, one big
opening confluent with orbit
Beak instead of teeth; premaxilla & dentary elongated
 Splanchnocranium- similar to reptiles
 Pivoting quadrates allow cranial kinesis although
ectopterygoids are absent, and immobile
parasphenoid is fused to basisphenoid.
 When quadrate is pushed forward, the motion is
transmitted to upper beak via a movable palate, a
movable zygomatic arch, or both.
MAMMALS
Neurocranium:
 Larger, fewer bones due to fusion;
sutures found between skull bones
 Skull increasingly domed as
cerebral hemispheres increase is
size
 Neurocranium is incomplete
dorsally, resulting to fontanels (a
bregmatic bone ossifies and forms
an anomaly in human skulls)
 Petrosal (periotic) bones form in
the otic capsules
 2 occipital condyles
Dermatocranium:
 Decreased number of
bones
 Synapsid skull; zygomatic
arch varies from massive to
slender, even incomplete in
insectivores
 Air-filled cranial sinuses:
frontals sinuses extend into
horns; sinusitis is a
common aliment in humans
 Present in Homo erectus
and Mongolians, is a
postparietal or Inca bone
 Temporal complex has intramembranous and
endochondral origin:
1. Squamous portion- squamosal of lower
tetrapods
2. Tympanic bulla- unique to mammals and
encloses the middle ear; tympanic bone
surrounds the eardrum, entotympanic bone
represents the bulla
3. Petrous portion- ossified otic capsule
4. Mastoid portion- new in mammals; dorsal
part of hyoid arch may fuse to mastoid to
form styloid process

Tympanic and petrous portions unite to form
petrotympanic bone
Squamosal
Mastoid
Otic capsule
Tympanic bulla
Pterygoids become
reduced as winglike
processes of the
sphenoid
3 pairs of turbinal bones
(nasal conchae) develop
in the nasal
passageways: superior
concha is covered with
olfactory epithelium; the
2 lower conchae are
covered by nasal
epithelium with venous
plexuses that warm the
air en route to the lungs
Squamosal articulates with dentary bone,
which is sole lower jaw bone
Splanchnocranium: unossified tips of palatoquadrate and Meckelian cartilages give rise to
middle ear ossicles, along with the columella:
 quadrate becomes incus
 articular becomes part of malleus
 hyomandibula has already became stapes
Hyoid apparatus
and larynx:
 Consists of a
body & 2 or 3
horns (cornua);
 Anchors tongue,
provides
Attachment for
some extrinsic
muscles of
larynx
 Site of
attachment of
muscles that aid
in swallowing
In addition
to cricoid
and
arytenoid
cartilages
common to
tetrapods,
mammals
have
thyroid
cartilages
arising
from the
4th and 5th
arches
ARCH
SHARK
TELEOST
FROG
REPTILE
MAMMAL
1
Palatoquadrate
Meckel’s
cartilage
Quadrate
Epipterygoid
Metapterygoid
Articular
Quadrate
Ammulus
tympanicus
Articular
Mentomeckeli
an
Quadrate
Epipterygoid
Articular
Incus
Alisphenoid
Malleus
2
Hyomandibula
Ceratohyal
Basihyal
Hyomandibula
Symplectic
Interhyal
Epihyal
Ceratohyal
Hypohyal
Basihyal
Columella
(stapes)
Anterior horn
of hyoid
Body of hyoid
Columella
(stapes)
Anterior horn
of hyoid
Entoglossus
Columella
(stapes)
Styloid
process
Body of hyoid
3
Pharyngobranchial
Epibranchial
Ceratobranchial
Hypobranchial
Pharyngobranchial
Epibranchial
Ceratobranchial
Hypobranchial
Body of hyoid
2nd horn of
hyoid
Body of hyoid
2nd horn of
hyoid
Body of hyoid
4
Branchial skeleton
Branchial skeleton
2nd horn of
hyoid
Last horn of
hyoid
Thyroid
cartilages
5
Branchial skeleton
Branchial skeleton
Cricoid and
arytenoids
Cricoid and
arytenoids
Cricoid and
arytenoids
6
Branchial skeleton
Branchial skeleton
Not present
Not present
Not present
7
Branchial skeleton
Branchial skeleton
Not present
Not present
Not present







EVOLUTIONARY CHANGES IN
MAMMALIAN SKULL:
Loss of connection between head and pectoral
girdle to create neck in primitive tetrapods
Increasing skull strength through simplification by
loss of bones and articulations
Braincase evolution reflecting enlarged brain
Changes in sense organs (e.g., in median pinealparietal eye complex and loss of pineal foramen)
Development of secondary palate and respiratory
passages
Temporal fenestration and jaw adductor
differentiation
Change from quadrate-articular to dentarysquamosal jaw joint with concomitant development
of three middle ear bones
 Homologies among bones are difficult to
establish
 Sagittal section through skull of ancestral
amniote and mammal to show evolution of bones
that form braincase; note that the epipterygoid
of the primitive amniote splanchnocranium is
homologous with alisphenoid in mammals.
REGIONAL SERIES OF
DERMATOCRANIAL BONES
IN EARLY TETRAPOD
DERMAL ROOF
BONES LOST IN
MAMMALS:
Circumorbital series:
prefrontal,
postfrontal,
postorbital
Temporal series:
intertemporal,
supratemporal,
tabular (?)
Cheek series:
quadratojugal
Lower Jaw: splenials,
surangular,
coronoids
TEETH: teeth of vertebrates are homologous to the
placoid scale of elasmobranchs.
Usually of simple form and all alike among lower
tetrapods, they become heterodont (several kinds),
and thecodont (set in sockets in jaw bones).
Borne in lower tetrapods on various jaw and palatal
bones, they become limited in higher ones to the jaw
margins.
Teeth of mammals: incisors, canines, premolars,
molars; juvenile (no molars), and permanent sets
Trituberculate theory of mammalian tooth origin: 2
cusps arising from a ridge (cingulum) from neck of
tooth are added to simple reptilian tooth. Teeth of
upper jaw are slightly behind those of lower jaw.
HUMAN AND ANTHROPOID APE SKULL:
 large, rounded cranial portion
 flattened facial portion, vertical orientation
 complete separation of the orbits from the
temporal fossae
 reduction of the nasal cavities and
turbinals
 large mastoid process
 absence of a tympanic bulla
 extensive fusions of the skull bones
 unspecialized teeth: 2 incisors, slightly
enlarged canines, bunodont (separated
rounded cusp) molars
1. Name the bones of the neurocranium of a
basal craniate, and their fused derivatives.
2. What major steps occurred in the
phylogenetic development of the “complete” cranium?
3. Tabulate: regions of ossification in the cranium, and the bones
present in each region of the teleost, amphibian, reptilian, and
mammalian skulls.
4. Tabulate: pharyngeal arches of basal vertebrate, and their
homologues in teleost, amphibians, reptiles, mammals
5. Tabulate: dermal bones in each of these regions of the teleost,
amphibian, reptilian, mammalian skull: roof, upper and lower
jaw, palate
6. Describe the phylogenetic patterns for the craniate temporal
fossae, and their fuctional role in each group.
7. Name the bones that contribute to the formation of the primary
and secondary palate.
8. List the types of jaw suspension, and their participating bones.
9. Discuss the phylogeny of the mammalian middle ear bones.
10.What is the functional significance of cranial kinesis?

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