Cranial skeleton Flashcards
What are the three main components of the cranial skeleton?
chondrocranium: base of the braincase
splanchnocranium: visceral arches
dermatocranium: outer part of the braincase
What are the 3 skull modifications: temporal fenestrae/fossae?
anapsid: no fenestrae
synapsid: pair of 1 fenestra
diapsid: pairs of 2 fenestrae
Which vertebrates are anapsids?
fish and turtles
Which vertebrates are synapsids?
mammals
Which vertebrates are diapsids?
some reptiles and birds
What is the proposed purpose for temporal fenestrae/fossae?
location for jaw muscle attachment
T or F: the chondrocranium is a single piece
true, but it’s made of numerous fused bones
WHat are the major bone groups in the chondrocranium?
occipitals, sphenoids, ethmoids
What is the chondrocranium derived from?
mesodermal sclerotome and neural crest cells
In the embryo, paired cartilages underneath the brain develop into what two things?
parts of the cranium to support the brain
the roof of the mouth or primary/hard palate
What are the sense organs housed in during embryonic stage?
cartilage capsules
What forms around the brain during development beginning at the notochord?
cartilage
When sense organs are surrounded by cartilage during development what 3 things do they form?
the optic capsule (eyes)
the otic capsule (ears) - if present
the nasal capsule (olfactory)
Which two cartilage capsules encasing sensory organs fuse to the chondrocranium?
the nasal and otic capsules
What is the sclera? What is its purpose?
the optic cartilage forms the sclera instead of fusing to the chondrocranium
it contains cartilage or bone
allows movement of the eyes
How many pairs of cartilages make up the human chondrocranium?
6
What are the 6 paired cartilages in the human chondrocranium?
parachordal cartilages - forms around notochord
prechordal cartilages- forms in front of notochord
occiptal cartilages- forms where the brain meets the spinal cord
otic capsule - forms inner ear
orbital cartilages - forms eye
nasal capsules - forms olfactory organ
What does the splanchnocranium contribute to?
jaws
forms the gill arches, hyoid, and cartilages at anterior end of trachea, glottis, epiglottis, larynx
What does the splanchnocranium develop from?
visceral arches that provide gill support in fishes
what is the visceral skeleton derived from?
splanchnic (gut) mesoderm, neural crest cells
What is the purpose of the pharynx?
involved in feeding
in lesser derived: in respiration
T or F: more derived vertebrates have less gill slits - why/why not?
true
they have evolved away from filter feeding
What is another name for visceral arches?
gill bars
What is the mandibular arch derived from?
the first visceral arch
What are jaws mainly derived from?
the mandibular arch
T or F: jaws are modified gill supports
true, they are derived from the mandibular arch which is derived from the first visceral arch (gill slits)
What are the two components of the mandibular arch?
the mandibular cartilage (lower jaw)
palatoquadrate cartilage (upper jaw)
What is the hyoid arch?
the second visceral arch
in tetrapods, what purpose does the hyoid arch/2nd visceral arch serve?
supports the jaw and tongue
What is the tongue attached to?
hyoid bone
In tetrapods, which part of the tongue/hyoid articulates with the chondrocranium?
the dorsal part = the hyomandibula (remember in the frog dissection, the tongue was attached at the dorsal end of the mouth, not the anterior like ours)
What did visceral arches 3-7 become? what do they do?
branchial arches
involved in respiration
What 2 arches work together to allow jaw movement?
mandibular and hyoid arches
What are the 3 the mandibular and hyoid arches can be articulated with the chondrocranium? what vertebrate groups have these styles?
amphistylic - early cartilaginous and early bony fishes
hyostylic - elasmobranchs and most bony fish
autostylic - lungfishes and tetrapod ancestors
Describe amphistylistic articulation. what are the vertebrate groups that have this?
jaw is directly connected to chondrocranium and is supported by hyomandibula
early cartilaginous fish
early bony fish
Describe hyostylistic articulation. what are the vertebrate groups that have this?
upper and lower jaw supported only by hyomandibula
upper law has no connection to chondrocranium
elasmobranchs and bony fishes
Describe autostylistic articulation. what are the vertebrate groups that have this?
upper jaw is either articulated or fused with the chondrocranium
lower jaw forms mandibular cartilage
jaw not supported by hyomandibular
lungfish
tetrapod ancestors
what is the dermatocranium?
bones that:
compose the roof of the cranium (outer braincase)
cover the major sense organs and brain
form plates and armour for some vertebrates
Where does the dermatocranium develop?
within the dermal layer of the skin
T or F: dermatocranium, like the chondrocranium and splanchnocranium is made up of bones that are preceded in development by cartilages?
false
they are not preceded by cartilages
What are the dermal bones in ostracoderms?
the original dermal scales (armour) which sink into and attach to the neurocranium and become ossified
What does ossified mean?
turned into bone
What are dermal bones derived from?
neural crest cells
What are formina? singular: foramen
collective name for the various small openings in the skull
aka fenestrae
What is the purpose of foramina?
they are openings for the series of 10 paired cranial nerves to connect to the brain and major sense organs, facial muscles, tongue, teeth, etc
What are cranial sutures?
an immovable, fibrous joint in the skull
bone surfaces are closely connected by connective tissue
What are the 4 types of cranial sutures?
coronal - between frontal bone and 2 parietal bones
sagittal - between 2 parietal bones
lambdoidal - between right and left parietal bones and occipital bone
squamosal - between parietal and temporal bone on each side
What are Wormian bones? where are they located?
small bone fragments located in sutures
especially found in sagittal and lambdoidal
What are 2 skull modifications for more powerful jaws?
otic notch
temporal fossae
How does the otic notch increase jaw power?
the otic notch is an adaptation for muscle attachment to compensate for increased jaw muscles and counter dermal bone
Are turtles anapsids or diapsids?
they were thought to be anapsid, but new evidence suggests that like their reptilian relatives, they’re diapsids
How do temporal fossae/fenestrae increase jaw power?
paired openings on the skull create an attachment location for larger jaw muscles
What are the two possible temporal fenestrae?
infratemporal and supratemporal
In what two ways can the eye orbital be related to the temporal fenestrae/fossae?
the eye orbit can be separate from fossae - ex. cats, horses, humans
or
can be merged - ex. wolves, rats
What was a major skull modification for breathing air?
evolution of the secondary palate
What are the 3 stages of secondary palate evolution?
primary unmodified palate = complete roof to the mouth - fishes and amphibians
partial secondary palate = a trend toward the evolution of the secondary palate - some bones developed (ex. maxilla, premaxilla, palatine) - some reptiles (not birds)
complete secondary palate =
alligator has complete bony
mammals have complete not bony
birds have complete fleshy
How can amphibians live on land if their palate is primary and unmodified for breathing air (ie., complete roof)?
they use cutaneous respiration and perform gas exchange across their skin for respiration
What type of secondary palate do alligators have?
complete bony
What type of secondary palate do birds have?
complete fleshy
What type of secondary palate do mammals have?
complete function - both bony and fleshy components q
Why do birds have complete fleshy secondary palates instead of bony like their reptilian relatives?
to save weight
What are fontanels? what is their function?
membrane-filled soft spots in mammalian skulls present only while developing which later are filled in with bone
function:
connect the incomplete cranial bones during development
allow the head to change shape during birth to fit through narrow birth canal
allow rapid growth during first 2 years of development
how many middle ear bones do mammals have? reptiles, amphibians?
mammals = 3
reptiles, amphibians = 1
What are turbinal bones?
pairs of rolled up bones covered in olfactory epithelium usually located in the nose of animals to increase surface area for smelling
Why is the evolution of jaws so significant for vertebrates?
allowed them to capture and eat larger food
How is the evolution of the jaw related to the size of vertebrates?
being able to eat larger food more quickly allowed vertebrates to grow in size faster than invertebrates
which vertebrates have upper jaws that are not fused to the chondrocranium? what does this allow?
some fish, like sharks can move their jaws independently of their skull
Why does it appear like sharks can dislocate their upper jaw from the skull when they open their mouth to catch prey?
the upper jaw is not united to the chondrocranium and can therefore move independently of the skull
What is the function of the hyoid bone?
it supports the tongue
also attaches to muscles of the phayrnx and neck
How is a swinging jaw an advantageous adaptation?
a swinging jaw is not fused to the cranium so it allows the mouth to open wider and for the animal (fish) to catch larger prey and provides a stronger bite
What bones comprise the upper and lower jaws in mammals?
upper: palatoquadrate cartilage of the mandibular arch
lower: the dentary bone (just one bone)
What does the hyomandibular do in fishes?
What does the hyomandibular become in reptiles and amphibians?
the only middle ear bone
What does the hyomandibular become in mammals?
becomes a bone in the middle ear
What do the articular and quadrate bones become in mammals?
each becomes a bone in the middle ear
How many middle ear bones do mammals have? reptiles and amphibians?
mammals = 3, from the hyomandibular, articular, and quadrate
reptiles and amphibians = 1 from the hyomandibular
