Skeletal System - The Skull Flashcards
Skeletal framework of the head
Skull = cranium = head skeleton
the skulll of vertebrates are composed of these
Main braincase, the cranium (neurocranium) which surrounds and protect the brain
Sense capsules associated in development with the olfactory, auditory and visual sense organs
Numerous components of the visceral skeleton
the skull is composed of three originally independent units:
Neurocranium or primary braincase
Dermatocranium
Splanchnocranium or visceral skeleton
part of the skeleton that is loosely associated in early vertebrates and closely associated in amniotes
skull
Components of the Cranium
Cartilage or endochondral bone
Floor and wall of braincase and sense capsules
Neurocranium
Components of the Cranium
Membrane or dermal bone but never cartilage nor endochondral bone
Superficial covering of the skull (roof and sides of skull and parts of the mandible)
Dermatocranium
Components of the Cranium
Cartilage or endochondral bone
Part of the visceral skeleton (gill arches) associated with the skull
Mostly visceral arches I and II
Splanchnocranium
Components of Splanchnocranium
composed of the embryonic upper jaw cartilage and its replacement bones
Embryonic lower cartilage and its replacement and investing bones
Components of the Cranium
Protects the brain and certain special sense organs
Arises as cartilage
Subsequently partly or wholly replaced by bone except in cartilaginous fishes
Neurocranium
how is the Neurocranium formed
Starts as several independent cartilages that later expand and unite to form a cartilaginous braincase
Embryology process
After the formation of the embryonic brain, the mesenchyme differentiate to form a membranous layer called the membranous cranium
The notochord extends forward beneath the brain, terminating near the infundibulum
The membranous cranium surrounds the anterior portion of the notochord
The parachordal plates are located lateral to the notochord and otic capsules
Prechordal cartilages formed in front of the parachordals
The ventral region of the membranous cranium will become the ______
neurocranium
Neurocranium begins as pair of ______________ cartilages below the brain
parachordal and prechordal cartilages
plates that are located lateral to the notochord and otic capsules
parachordal plates
expand and join along with the notochord to form the basal plate enclosing the tip of the notochord and later becomes the floor beneath the midbrain and the hindbrain
Parachordal cartilages
______________ formed in front of the parachordals
Prechordal cartilages
cartilages expand and join to form an ethmoid plate that later will become the rostrum
Prechordal
contributes to the formation of the internasal septum between the nasal capsules
rostrum
Simultaneou with the formation of cartilages, three pair of capsules are formed from the developing sense organs:
Nasal capsules from the olfactory sense organ
Otic capsules from the auditory sense organ
Optic capsules from the optic sense organ
fuses with olfactory capsules and the basal plate fuses with otic capsules to complete the roof, sides and floor of the brain
ethmoid plate
unite posteriorly leaving a prominent opening in the center, the hypophyseal fenestra, where the pituitary gland lies
prechordals and parachordals
Endochondral ossification occurs more or less simultaneously at 4 regional ossification centers:
Occipital
Sphenoid
Ethmoid
Otic
Cartilage surrounding the foramen magnum can be replaced by as many as 4 bones:
Supraoccipital bone dorsally
Exoccipital bones laterally
Basioccipital bone ventrallly
One or more of the 4 may remain cartilaginous in what modern class of vertebratesn
modern amphibians
Cartilage surrounding the foramen magnum can be replaced by as many as 4 bones and All four bones fuse in mammals to form a single bone called the
occipital bone
Articulation of the neurocranium with the 1st vertebra is via the ________
occipital condyles
what class have a single condyle borne out of the basioccipital bone
Stem amphibians
two classes that have a single condyle
Living reptiles and birds
two classes that have shifted the condyle to the two exoccipitals
Modern amphibians and mammals
what centers Osssifies independently in the synapsid and reptilian lineages
Sphenoid Centers
sphenoid that forms from the cartilage underlying the midbrain and pituitary gland
Basisphenoid
sphenoid that ossifies anterior to the basisphenoid in mammals
Also contributes to the sidewall above the basisphenoid
Presphenoid
sphenoid bone (crocodiles and dinosaurs) forms the lateral ossification of the sphenoid redion
Laterosphenoid
sphenoid bone (archosaurs) forms a separate interorbital septum
Orbitosphenoid
sphenoid bone helps to form the lateral wall in some mammals though it is derived from the palatoquadrate cartilage
Alisphenoid
Sphenoid Centers
Basisphenoid, presphenoid, alisphenoid, Laterosphenoid, Orbitosphenoid
mammals can form a single sphenoid bone with wings
Basisphenoid, presphenoid and alisphenoid
Lies anterior to the sphenoid and includes the _________ and olfactory capsules
Tends to remain cartilaginous in tetrapods from amphibians to mammals
Ethmoid Centers
No replacement bones develop above the brain
true
Pituitary gland rests on the ________ of the basisphenoid regions
tella surcica
Most basal tetrapods develop no ____________ whatsoever
ethmoidal ossification centers
Ossification centers in amniotes are chiefly _____________
mesethmoid bones
Ossification centers in amniotes are chiefly mesethmoid bones contribute to:
Cartilaginous nasal septum of birds and mammals and the anterior portion of interorbital septum in birds
One or more scroll-like turbinal bones (conchae) of most reptiles, birds and mammals
Cribriform plate perforated by olfactory foramina in mammals
in anurans is the sole bone arising in the ethmoid and sphenoid regions
Sphenethmoid
develops in the lateral walls of the nasal passageway of Sphenodon
Ectethmoid
cartilages found in the nasal passages are not from ethmoid ossification
Winglike alar bone and small sesamoid cartilages
capsule surrounding the membranous labyrinth becomes the prootic, opisthotic and epiotic
Otic capsule
One or more may unite with adjacent replacement of mebrane bones
Otic Centers
fuse with exoccipitals in frogs and nonavian reptiles
Opisthotics
unite to form a single periotic or petrosal bone in mammals
Prootic, opisthotic and epiotics
may unite with the squamosal to form a temporal bone
Petrosal bone
Occipital bones in
Fishes (Teleost)
Amphibians
Reptiles/Birds
Mammals
Supraoccipital
Exoccipital
Basioccipital
Mesethmoid bone is present in what classes
Mammals (ethmoid)
(absent in primitive mammals and ungulates)
Fishes (Teleost)
Ethmoid region in
Fishes (Teleost)
Amphibians
Reptiles/Birds
Mammals
is ossified, unossifed, or turbinals
Fishes (Teleost) - ossified
Amphibians - unossifed
Reptiles/Birds - unossifed
Mammals - turbinals
are these sphenoid bones present in each class
Sphenethmoid
Orbitosphenoid
Basisphenoid
Pleurosphenoid
fish
Sphenethmoid
Orbitosphenoid
Basisphenoid
Pleurosphenoid
ampibhians
Sphenethmoid
Orbitosphenoid
Basisphenoid
Aves, Reptiles
Sphenethmoid
Orbitosphenoid
Basisphenoid
Pleurosphenoid (crocodiles and amphibians)
Mammals
Sphenethmoid
Orbitosphenoid
Basisphenoid
Laterosphenoid is only present in what animal
snake
whatotic capsule perotic part is present in what classes
Fishes (teleost)
Prootic
Epiotic
Sphenotic
Amphibians
Prootic
Opisthotic
Aves
absent
Reptiles
Prootic
Epiotic
Sphenotic
Mammals
Petrosal withvmastoid process
This bone is of dermal origin, so it is not strictly homologous to tetrapod _________.
mesethmoid
This bone is usually absent or reduced in some fishes.
Basisphenoid
Associated with the filter-feeding surfaces
Generally supports the gills and offer attachment for respiratory muscles
Contributes to the jaws and hyoid apparatus of gnathostomes
May remain cartilaginous or become covered by dermal bones
Splanchnocranium
Declines in importance in tetrapods but never disappears
Splanchnocranium
Each visceral arch consists of a:
Skeleton
Branchiomeric muscle
Cranial nerve
Aortic arch
Gill filaments
came from neural crest cells departed from the sides of the neural tube and migrate into the walls of the pharynx between successive pharyngeal slits
Differentiate into respective pharyngeal arches
Blastemas
are associated with their respiratory gill system called branchial or gill arches in aquatic vertebrates
Pharyngeal arches
Each arch is composed of a series of up to five articulated elements on each side (from dorsal to ventral):
Pharyngobranchial
Epibranchial
Ceratobranchial
Hypobranchial
Basibranchial
The first fully functional arch of the jaw is the ____________, which is the largest and most cranial
Composed of the dorsal palatoquadrate and ventral Meckel’s cartilage
mandibular arch
The arch that follows the mandibular arch composed of the myomandibula
hyoid arch
Mouth of agnathans is not supported by jaws
The __________ supports the roof of the pharynx and lateral pharyngeal slits
splanchnocranium
agnathan fish that were restricted to a diet of small particulate food
Ostracoderms
adaptation in agnathans for eating food
In some groups, small teeth-like structures derived from the surface scales, surrounded the mouth and used to scrape rocks for food
The mucus-lined walls of the pharynx collected these scraped food particles from the passing stream
Jaws first appeared in ____________ that used them as food traps or as crushing or chewing devices to process food in the mouth
acanthodians and placoderms
The branchial arches gave rise to jaws as proposed by two separate theories on its origin:
Serial theory
Composite theory
what theory says that the jaws arise completely from one of the cranial branchial arches
Elements may be lost within it, but other elements from other arches do not contribute
Serial Theory
the theory that imples that the mandibular arch is formed from elements of several adjacent arches that also contribute to the neurocranium
The palatoquadrate forms from the fusion of the epibranchial of the premandibular arch with the epibranchial and pharyngobranchial of the mandibular arch
Meckel’s cartilage arises from the enlarged ceratobranchial element
Hyoid arch arises from the epibranchial, ceratobranchial and hypobranchial elements of the 3rd gill arch
The other elements of the primitive arches are lost and fused to the neurocranium
Composite Theory
Types of Jaw Attachment
Paleostylic
Euautostylic
Amphistyly
Hyostyly
Metaautostyly
Craniostyly
Characteristic of agnathans
None of the arches attach directly to the skull
Paleostylic
Found in placoderms and acanthodians
Mandibular arch is suspended from the skull by itself without the aid from the hyoid arch
Euautostylic
Found in early sharks, some osteichthyans and crossopterygians
Attached to the braincase through two primary articulations
Cranially by a ligament connecting the palatoquadrate to the skull
Caudally by the hyomandibular
Amphistyly
Found in most bony fishes
The mandibular arch is attached to the braincase primarily through the hyomandibula with the aid of the symplectic bone
Hyostyly
Found in most amphibians, reptiles and birds
Attached to the braincase directly through the quadrate bone
Formed in the caudal part of the palatoquadrate
Metaautostyly
Found in mammals
The entire upper jaw is part of the braincase but the lower jaw called dentary bone is suspended from the dermal squamosal bone of the braincase
The palatoquadrate and Meckel’s cartilages remain cartilaginous except at their posterior ends which becomes the incus and malleus of the middle ear respectively
Craniostyly
Earliest vertebrates are encased in bony dermal armor and the extent to which it covers the body is variable
Bony plates are present in the head
Dermatocranium