mrs. ofelia solano saludar department of natural sciences university of st. la salle bacolod city
TRANSCRIPT
SKELETAL SYSTEM: SKULL & VISCERAL
SKELETON
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)
1. CHONDROCRANIUM or NEUROCRANIUM 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.
2. DERMATOCRANIUM
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, post- parietals
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: para- sphenoids, vomer palatines, pterygoids, ectopterygoids (cover palato- quadrate)
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.
3. SPLANCHNOCRANIUM 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
3. FORMATION OF THE COMPLETE SKULLCENTERS 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 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 CENTERS
Occipital condyles are projections by which the skull articulates with the atlas.
Fishes and primitive tetra- pods 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.
SPHENOID CENTERS 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.
ETHMOID CENTERS
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)
PLACODERMS
PHYLOGENY OF THE VERTEBRATE SKULL
CROSSOPTERYGIANS- the dermatocranium forms a series of paired and unpaired bones along mid-dorsal line of skullLABYRINTHODONTS- 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
CHONDRICTHYESChondrocranium: 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 regiono 2 occipital condyles
Splanchnocranium: larval stages have fish-like gills supported by gill archeso 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
REPTILESNeurocranium: 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 orbitBeak 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.
MAMMALSNeurocranium: 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
tetrapods2. 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 capsule4. 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
Tympanic bulla
Squamosal
Mastoid Otic capsule
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 palato-quadrate 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 PalatoquadrateMeckel’s cartilage
QuadrateEpipterygoidMetapterygoidArticular
QuadrateAmmulus tympanicusArticularMentomeckelian
QuadrateEpipterygoidArticular
IncusAlisphenoidMalleus
2 HyomandibulaCeratohyalBasihyal
HyomandibulaSymplecticInterhyalEpihyalCeratohyalHypohyalBasihyal
Columella (stapes)Anterior horn of hyoidBody of hyoid
Columella (stapes)Anterior horn of hyoidEntoglossus
Columella (stapes)Styloid processBody of hyoid
3 PharyngobranchialEpibranchialCeratobranchialHypobranchial
PharyngobranchialEpibranchialCeratobranchialHypobranchial
Body of hyoid 2nd horn of hyoidBody of hyoid
2nd horn of hyoidBody 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 pineal-
parietal 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 dentary-
squamosal 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, postorbitalTemporal series: intertemporal, supratemporal, tabular (?)Cheek series: quadratojugalLower 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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