09 skull and visceral skeleton
TRANSCRIPT
Comparative Anatomy of the Vertebrates:
[CHAPTER 9:
Skull and Visceral Skeleton]
CRANIAL SKELETON (SKULL)
Neurocranium
Dermatocranium
VISCERAL SKELETON
palatoquadrate
Meckel’s cartilage
branchial arches
I. NEUROCRANIUM
“endocranium”, “chondrocranium”, “primary
braincase”
endoskeleton
part of the skull that:
protects the brain and sense organs
arises as cartilage
partly or wholly replaced by bone
(except in cartilaginous fishes)
A. FORMATIVE CARTILAGES OF THE
NEUROCRANIUM:
1. PARACHORDAL CARTILAGE
parallel the anterior end of the notochord
beneath the midbrain and hindbrain
basal plate
origin: sclerotome or epimeric mesoderm
2. PRECHORDAL CARTILAGES
“trabeculae cranii”
develop anterior to the notochord
underneath the forebrain
ethmoid plate
origin: neural crest ectoderm
3. SENSE CAPSULES
olfactory capsule – partially surrounding
the olfactory epithelium
otic capsule – completely surrounding
the otocyst; anteriorly incomplete
optic capsule – forms around the retina;
“sclerotic coat of the eyeball”; unfused
from the neurocranium
OUTLINE
I. Neurocranium
A. Formative Cartilages
1. Parachordal Cartilages
2. Prechordal Cartilages
3. Sense Capsules
B. Floor, Walls , Roof
1. Hypophyseal Fenestra
2. Tectum
C. Neurocrania of Adult Craniates
a. Living Agnathans
b. Chondrichtyes
c. Teleost
D. Ossification Centers
1, Occipital
2. Sphenoidal
3. Ethmoid
4. Otic
II. Dermatocranium
A. Dermal Bones of Primitive Tetrapod
1. Roofing
2. Marginal
3. Primary Palatal
4. Opercular
B. Neurocranial-Dermatocranial Complex
a. Teleosts
b. Amphibians
c. Non-Avian Reptiles
- Temporal Fossa
- Secondary Palate
- Cranial Kinesis
d. Birds
e. Mammals
III. Splanchnocranium
a. Living Agnathans
b. Elasmobranchs
- Jaw suspension
c. Teleosts
d. Tetrapod
- Amniote Hyoid
- Laryngeal Skeleton
Comparative Anatomy of the Vertebrates:
[CHAPTER 9:
Skull and Visceral Skeleton]
B. FLOOR, WALLS, ROOF
1. HYPOPHYSEAL FENESTRA
accommodates the hypophysis and internal
carotid arteries
2. TECTUM
cartilaginous roof above the brain with one
or two prominent fenestrae
primitive craniates condition
C. NEUROCRANIA OF ADULT CRANIATES
a.) LIVING AGNATHANS
neurocranium components are
independent
notochord not fused with the basal plate
unchondrified, fibrous tectum
b.) CHONDRICHTHYES
chondrocranium
walls are fully developed
posterior occipital wall in gnasthostomes
brain completely roofed by cartilage
hypophyses cradled by the sella turcica
occipital condyle
endolymphatic fossa
endolymphatic and perilymphatic ducts
c.) TELEOSTS
cartilaginous neurocranium is replaced
by endochondral bone through
ossification
C. OSSIFICATION CENTERS
1. OCCIPITAL
BASIOCCIPITAL – underlying the
hindbrain; formed by OC ventral to the
foramen magnum
EXOCCIPITAL (2) – lateral walls of the
FM
SUPRAOCCIPITAL – above the FM
occipital bone (fusion of all 4 occipital
elements) in mammals
OCCIPITAL CONDYLES
mammals, modern amphibians - 2
exoccipitals
stem amphibians - 1, borne on the
basioccipital
reptiles, birds – 1
2. SPHENOID
ossification occurs independently in
synapsid and reptilian lineages
BASISPHENOID – ossified cartilaginous
neurocranium and pituitary gland;
anterior to the basioccipital
PRESPHENOID – anterior to the
basisphenoid
LATEROSPHENOID – lateral
ossification in archosaurs
ORBITOSPHENOID – separate
interorbital septum in archosaurs
ALISPHENOID – helps form the lateral
wall; derived from the palatoquadrate
cartilage (splanchnocranium)
sphenoid bone with “wings” (fusion of
basisphenoid, presphenoid, alisphenoid) in
mammals
3. ETHMOID
anterior to the sphenoid
ethmoid plate and olfactory capsule
tends to remain cartilaginous in tetrapods
from amphibians to mammals
no ethmoidal ossification for basal tetrapods
wing-like alar and sesamoid cartilage,
though part of the nasal passageway, are
not derived through ethmoid ossification
MESETHMOID – chief amniote OC
nasal septum
anterior interorbital septum
turbinal bone or conchae
cribriform plate in mammals
SPHENETHMOID – sole bone arising in
the sphenoid and ethmoid region in
anurans
Comparative Anatomy of the Vertebrates:
[CHAPTER 9:
Skull and Visceral Skeleton]
ECTETHMOID – develops in the lateral
walls of the nasal passageway of the
Sphenodon.
4. OTIC
PROOTIC – anterior
OPISTHOTIC – posterior
EPIOTIC - above
PETROSAL (PERIOTIC) BONE – fusion of
all 3 otic elements in birds and mammals
opisthotic fuse with the exoccipital in
amphibians and non-avian reptiles
TEMPORAL BONE – fusion of petrosal and
squamosal
FONTANEL – membranous soft spot in the dorsal portion of the neurocranium
dense fibrous connective tissue
advantage: temporary mishapening during passage of infant in the birthcanal
BREGMATIC BONES – ossified fontanel
II. DERMATOCRANIUM
membranes of the skull
vestiges of the ancient dermal armor
external to the brain case
surrounds the neurocranium
homologous: dermal armor of ostracoderms (cephalaspids)
exoskeleton
ossify from DERMAL MESENCHYME (primitive) or SUBDERMAL MESENCHYME (modern vertebrates)
A. DERMAL BONES OF PRIMITIVE TETRAPOD
1. ROOFING BONES (-al)
bones that form above and alongside the brain and neurocranium
protective shield over the brain and sense organs
pattern: (1) rhipidistians: series of paired and unpaired scale-like bones along the middorsal line from the nares to the occiput, overlying neurocranium components; (2)
labyrinthodonths: series of paired dermoccipitals
VAULT SERIES: nasal, frontal, parietal, postparietal (collectively DERMOCCIPITALS)
ORBITAL SERIES: intertemporal, supratemporal, tabular, squamosal, quadratojugal
TEMPORAL SERIES: lacrimal, prefrontal, postfrontal, postorbital, infraorbital, jugal
2. MARGINAL BONES
dermal bones of the upper jaw
palatoquadrate cartilages as embryonic precursor of upper jaw of vertebrates
premaxilla, maxilla
3. PRIMARY PALATAL BONES (-pterygoid)
fishes: roof of the oropharyngel cavity
basal tetrapods: oral cavity
remains in the roof of the nasal passageway even after developing secondary palate
parasphenoid, vomer, palatine, endopterygoid, ectopterygoid
4. OPERCULAR BONES (-ulars)
flap of tissue arising as an outgrowth of the hyoid arch
extends caudad over the gill slits
operculum: membranous (holocephalans), absent (elasmobranch), stiffened by squamous plates (teleost)
GULAR BONES (basal fishes)
specialized as BRANCHIOSTEGAL RAYS (actinopterygians, dipnoans)
preoperculars, suboperculars, interoperculars, gulars
absent in tetrapods
PARIETAL FORAMEN – houses the median eye (fishes, amphibians, lizards)
B. NEUROCRANIAL-DERMATOCRANIAL COMPLEX
a.) TELEOST
largest number of dermatocranial bones
neurocranium fully ossified except for the olfactory capsules
Comparative Anatomy of the Vertebrates:
[CHAPTER 9:
Skull and Visceral Skeleton]
dermatocrania resemble Devonian
ancestor’s
dipnoans: large dermal bony plates
b.) AMPHIBIAN
flattened, platybasic skulls
incomplete neurocranium (dorsally) and dermatocranium
lost majority of its membrane bones
COLUMELLA: middle ear ossicle that conducts sound waves from an eardrum to the capsule
anurans: large palatal vacuities
apodans: least modified, rigid
c.) NON-AVIAN REPTILES
well-ossified neurocrania
single occipital condyle
mainly membrane bones
partial or complete secondary palate
lizards: parietal foramen
specializations:
1. TEMPORAL FOSSA
– cavernous opening in the temporal region of amniote skulls bounded by arches
– provide space and surfaces for accommodation of adductor muscles
Diapsid: crocodilians, Sphenodon,
archosaurs,
two pairs of TF (superior:
supratemporal + inferior:
zygomatic)
Synapsid: mammals
one pair of lateral TF
infratemporal arch (squamosal +
jugal)
zygomatic arches (human
cheeks)
Euryapsid: ichthyosaur, plesiosaurs
one pair of dorsally located TF
evolved from the diapsid type
with the loss of the ventral pair
Anapsid: turtle, stem reptiles
no TF, unperforated
Modified Diapsid: lizards, snakes, birds
cavernous void in the
posterolateral walls of the
squamate skulls due to loss of
arches
2. SECONDARY PALATE
– horizontal partition dividing the primitive oral cavity into separate oral and nasal passageways
– processes of the premaxillae, maxillae, and palatine bones; complete to the midline
– caudad only in crocodilians and mammals – PALATAL FISSURE (if secondary palate
in incomplete)
3. CRANIAL KINESIS
– “kinetism” – characteristic of teleosts, snakes, lizards, – due to reduction or loss of the arches and
acquisition of INTRACRANIAL JOINTS – food procurement – movement of one functional component of
the skull, independent of another component
d.) BIRDS
modified diapsid
mainly dermal bones
sutures obliterated except in ratites
thin, domed skulls
large orbits
elongated jaw, beak
e.) MAMMALS
single temporal fossa
dentary as sole mandibular bone
quadrate and articular became middle ear ossicles
expanded braincase
reduced dermatocranial bones
full complement of neurocranial bones
temoral complex
dorsally incomplete neurocranium (fontanel) III. SPLANCHNOCRANIUM
develops within the pharyngeal arches
Comparative Anatomy of the Vertebrates:
[CHAPTER 9:
Skull and Visceral Skeleton]
origin: neural crest blastemas
feeding structure
branchial respiration a.) LIVING AGNATHAN
no palatoquadrate, Meckel’s cartilage, or branchial arches
V-shaped LINGUAL CARTILAGE (dental plate): rasping tongue-like organ
cartilaginous branchial basket
b.) ELASMOBRANCHS
palatoquadrate, Meckel’s cartilage, hyoid cartilages, branchial cartilages, median ventral basihyal, basibranchial cartilages
c.) TELEOST
more complex hyoid skeleton than elasmobranchs
reduced caudalmost gill arches
palatoquadrate cartilage ensheathed by premaxilla and maxilla
roof of the oropharyngeal cavity develop two to three dermal ossification sites
ossification:
posterior palatoquadrate quadrate bone
caudal Meckel’s cartilage articular bone
remaining cartilage dentary, angular
ossification centers:
hyomandibular cartilage: SYMPLECTIC and INTERHYAL
ceratohyal: EPIHYAL JAW SUSPENSION
1. HYOSTYLY
– most elasmobranchs and teleost – hyomandibular cartilage is braced against the otic capsule – posterior end of the palatoquadrate cartilage braced against the hyomandibula
2. AMPHISTYLY
– primitive sharks – hyomandibula and processes of the palatoquadrate are braced independently against the braincase
3. AUTOSTYLY
– chimaeras, lung fishes, tetrapod – palatoquadrate is attached to the neurocranium
d.) TETRAPOD
modified functions:
hyoid arch: anchorage of tongue muscles
modified hyomandibula and jaws: sound transmission
laryngeal skeleton: support of vocal cords
modifications of the mandibular arch:
Quadrate bone INCUS (middle ear ossicle)
Meckel’s cartilage dentary, angular, surangular, splenial, coronoid, prearticular
posterior end of MC articular (excluding mammals), MALLEUS (mammals; middle ear ossicle)
dentary expansion
formation of RAMUS (insertion of temporalis)
new jaw joint in mammals
formation of ear ossicles
columella/ stapes – first ear ossicle; derived from the hyomandibula, specifically the dorsal tip of the hyoid arch
EVIDENCE: Meckel’s cartilage malleus
embryonic Meckel’s cartilage projects into the area where middle ear cavitaion is proceeding
MC’s cartilaginous posterior tip can be seen to separate, ossify and become the malleus
EVIDENCE: quadrate incus
articulation of the articular and quadrate bones in the diarthrosis
separation of the articular from the lower jaw
disappearance of the quadrate from the upper jaw
articulation of the articular in diarthrosis with the incus
AMNIOTE HYOID
anuran hyoid: derived from metamorphosis of branchial cartilages, hyoid arches, and gill-bearing arches
Comparative Anatomy of the Vertebrates:
[CHAPTER 9:
Skull and Visceral Skeleton]
amniote hyoid: derived from homologous
ANLAGEN, basihyal cartilages
snakes: no hyoid, vestigial branchial skeleton
lizards and birds: ENTOGLOSSUS, extends to a long darting tongue
mammalian hyoid:
cranial horns (second arch) – “greater horns”
tympanohyal = dorsal most and ends in a notch in the tympanic bulla
caudal horns (third arch) – “lesser horns”
stylohyal = embedded in the tendon of insertion of the posterior belly of the stylohyoid muscle
humans: ceratohyals (lesser horns); epihyal ang stylohyal (unossified stylohyoid ligament); tympanohyal (attached to the temporal bone)
anchors the tongue of tetrapods
skeleton for buccapharyngeal pressure
pump
respiration in anurans
attachment for extrinsic muscles of the
larynx
lower jaw movement
attachment of muscles for swallowing
LARYNGEAL SKELETON
cricoid and arytenoids cartilages (replacing
bones) = arise from the fifth pharyngeal arch
thyroid cartilages (in mammals) = arise from
the fourth and fifth pharyngeal arch