Lecture 10: Vertebrate Skeletal System Part II Flashcards
Describe how the vertebrate skull forms
- The skull forms the other part of the axial skeleton.
- It may be formed entirely of cartilage:
- In sharks, skates, and rays, remember that failure to replace cartilage with bone as the adult skeleton forms is an example of Neoteny.
- In all vertebrates the brain case develops in the embryo as an incomplete cartilaginous box with numerous openings (foramina) through which pass nerves and blood vessels to and from the brain.
- Additional cartilaginous capsules develop to enclose the special sensory organs such as the olfactory apparatus, eyes, and semicircular canals (balance).
What are the two main components of the vertebrate skull?
- Chondrocranium:
- Neurocranium: Cartilage and/or endochondral bone
- Splanchnocranium: Also referred to as the viscerocranium, this is the cartilage and/or endochondral bone - Dermatocranium: Dermal bone.
Describe the chondrocranium
The cartilaginous embryonic skull is the chondrocranium; it consists of:
- The braincase, or neurocranium:
- Includes three pairs of cartilaginous capsules housing special sensory organs:
- Olfactory (most anterior)
- Optic
- Otic(most posterior)
- The pharyngeal (gill) arches) or splanchnocranium
Describe the neurocranium
Floor forms from two pairs of cartilaginous plates:
- Parachordals (A): Flank the cranial end of the notochord.
- Prechordals (or Hypophyseals…should know both names)(B): Cranial to notochord and parachordals
- Posterior wall (D)
- Foramen magnum (E).
- Capules: Consist of the 3 following:
- Olfactory (F): Associated with sense of smell
- Optic (G): Associated with sense of sight.
- Otic (H): Associated with sense of balance
- Roof: Usually open, but closed in chondricthyes
- See Slide 7 for information on what the hell those letters mean
In the neurocranium, the Braincase is one of the endochondral ossification of the skull. Describe the braincase.
- Basioccipital: Below foramen magnum.
- Exoccipital: Paired laterally to foramen.
- Supraoccipital: Above foramen magnum.
- Basisphenoid (and presphenoid)…might be often fused to the occipital bone but I’m not certain.
- Stare hard at slide 8. Be able to recognize a neurocranium for what it is. (Slide 9)/
There are 6 pairs of arches in the splanchnocranium. Describe the first arch
First arch called Mandibular arch:
- Dorsal part = Palatopterygoquadrate bar:
- Ossifications = epipterygoids (alisphenoids in mammals)
- Ventral part: = Meckel’s cartilage.
- Ossifications =
- Quadrate (from Meckel’s cartilage)
- -And Articular
There are 6 pairs of arches in the splanchnocranium. Describe the second arch
Called The Hyoid Arch
- In many fishes, it braces the palatopterygoquadrate bar against the brain case.
- In most fish, the upper jaw is Not attached to the brain case (ours is). The hyoid arch pushes the bar (middle rod thing) up into the brain case. (Is the brain case the first arch?)
- Stare at the image on slide 10 until which arch is which is determined.
How does the chondrocranium in lamprey differ?
In cyclostomes, the embryonic-like cartilaginous skull persists in the adult as a complex basket-like framework of cartilage or calcified cartilage.
How does the chondrocranium differ in a shark?
- In chondrichthyes, the skull is represented by the chondrocranium. It is more complete than in cyclostomes, but it is still composed entirely Of cartilage.
- There are wing-like things on the mandibular arch which allows the shark to thrash it’s (unattached) jaws left and right in a saw-like motion when biting something.
Describe the dermatocranium
In fishes other than chondrichthyes and cyclostomes, a series of dermal bones covers the neurocranium and parts of the mandibular arch. Collectively this set of dermal bones is referred to as the dermatocranium.
Describe the are the lower jaw suspension differed in fish?
- The manner in which the lower jaw articulates with the braincase varies from one group of vertebrates to another.
- In elasmobranches the hyoid arch (derived from the second gill arch) braces the upper jaw against the neurocranium.
- = hyostylic style of articulation
- In holosteans, teleosts, and dipnoans, the chondrocranium shows varying degrees of ossification.
- Jaw articulation in these forms is usually hyostylic, but in lungfishes it is autostylic.
Describe the difference between hyostylic and autostylic articulation?
- Hyostylic:
- Example: Elasmobranchs, holosteans, teleosts, and dipnoans.
- Hyoid braces upper jaw against neurocranium.
- Autostylic:
- Example: Chimaeras and lungfishes.
- Upper jaw is fused to braincase.
- Jaw articulation is between quadrate and articular.
Review pictures and my notes on slide 15. I’m not gonna make a review slide, but should know to recognize whether a fish diagram is hyostylic or autostylic.
Describe the amphibian skull
- Primitive forms of tetrapods/amphibians:
- Had a boxlike dermatocranium.
- Modern forms of amphibians:
- Reduction of dermal elements
- Retention of considerable cartilage
- Paired occipital condyles (Can “nod” it’s head, but can’t rotate it.)
- Autostylic jaw articulation
- Hyomandibular= columella
Notes: Stapes has developed, but not other two inner ear bones (though there IS and inner ear cavity now). Eustachian tube leads to the throat.
What are the four Roof series in the dermal skull elements in primitive tetrapods?
Roof Series (In Order From Front to Back)
- Nasal
- Frontal
- Parietal
- Post-Parietal
What are the four Circumorbital series in the dermal skull elements in primitive tetrapods?
Circumorbital Series (Clockwise from top front to bottom front…or maybe not Clockwise, but you know what I mean)
- Prefrontal (Top Front of the eye)
- Post-orbital (Top back of the eye)
- Jugal (Bottom back of the eye)
- Lacrimal (Bottom front of the eye)
What are the Three Temporal series in the dermal skull elements in primitive tetrapods?
Behind the orbital series (from most cranial to caudal?)
- Intertemporal
- Supratemporal
- Tabular
These bones are usually lost to form the temporal bone
What are the three other series across the bottom of the dermal skull elements in primitive tetrapods?
From front to back
- Dentary
- Splenial
- Angular
What are the two Cheek series in the dermal skull elements in primitive tetrapods?
From Front to back behind the maxillary bone
- Quadratojugal
- Squamousal
Notes: The squamosal often forms the squamous part of the temporal bone
The quadratojugal may form part of the zygomatic arch.
What are the two tooth-bearing lateral series of dermal bones in the primitive tetrapod skull?
Forms the margins of the upper jaw
- Far front is the Premaxillary bone
- Followed by the maxillary bone.
What portions of the primitive tetrapod skull remain conserved in modern mammals?
- Dentary
- Maxillary
- Lacrimal
- Nasal
- Jugal
- Squamous
List 6 generalizations about the reptilian skull
- Reptilian skull, including the chonrocranium, is well ossified.
- Primitive forms had boxlike skulls, but modern forms have developed arches and openings
- Elements of dermatocranium are reduced in modern forms.
- Many of the reptilian dermal bones are homologous with mammal skulls.
- Single median occipital condyle.
- Jaw musculature well-developed: Related to development of increase in surface areas on sides of skull for muscle attachment and the development of the openings and arches.
Compare the reptilian skull arches and openings between anapsids and diapsids
- Anapsid:
- No arches and no additional openings.
- Found in cotylosaurs and turtles. …maybe
- Diapsid:
- Both lateral and dorsolateral openings
- Two arches
- Found in most reptiles:
- Both arches are present in Sphenodon.
- Lizards have lost the lower jaw.
- Snakes have lost both bars:
- This frees the quadrate and allows for a more movable lower jaw.
Compare the reptilian openings and arches between a euryapsid and a synapsid
- Euryapsid (Parapsid):
- May be a variant of a diapsid skull.
- Single dorsolateral opening bounded inferiorly by postorbital and squamosal bones.
- Found in plesiosaurs and icthyosaurs.
- Synapsid:
- Found in mammal-like reptiles and mammals.
- Single opening bounded inferiorly by the zygomatic arch.
What is one unique thing about the skull of anapsids?
There appears to be a large opening along the back of the skull on either side of the midline. This is basically an indentation in the back of the skull and is not comparable to the openings found in other reptilian skulls. This type of skull with the deep indentation is referred to as being emarginated.
