Lecture 10: Vertebrate Skeletal System Part II

Question 1

Describe how the vertebrate skull forms

Answer 1

• 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).

Question 2

What are the two main components of the vertebrate skull?

Answer 2

1. Chondrocranium:
   - Neurocranium: Cartilage and/or endochondral bone
   - Splanchnocranium: Also referred to as the viscerocranium, this is the cartilage and/or endochondral bone
2. Dermatocranium: Dermal bone.

Question 3

Describe the chondrocranium

Answer 3

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

Question 4

Describe the neurocranium

Answer 4

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

Question 5

In the neurocranium, the Braincase is one of the endochondral ossification of the skull. Describe the braincase.

Answer 5

• 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)/

Question 6

There are 6 pairs of arches in the splanchnocranium. Describe the first arch

Answer 6

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

Question 7

There are 6 pairs of arches in the splanchnocranium. Describe the second arch

Answer 7

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.

Question 8

How does the chondrocranium in lamprey differ?

Answer 8

In cyclostomes, the embryonic-like cartilaginous skull persists in the adult as a complex basket-like framework of cartilage or calcified cartilage.

Question 9

How does the chondrocranium differ in a shark?

Answer 9

• 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.

Question 10

Describe the dermatocranium

Answer 10

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.

Question 11

Describe the are the lower jaw suspension differed in fish?

Answer 11

• 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.

Question 12

Describe the difference between hyostylic and autostylic articulation?

Answer 12

• 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.

Question 13

Describe the amphibian skull

Answer 13

• 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.

Question 14

What are the four Roof series in the dermal skull elements in primitive tetrapods?

Answer 14

Roof Series (In Order From Front to Back)

1. Nasal
2. Frontal
3. Parietal
4. Post-Parietal

Question 15

What are the four Circumorbital series in the dermal skull elements in primitive tetrapods?

Answer 15

Circumorbital Series (Clockwise from top front to bottom front…or maybe not Clockwise, but you know what I mean)

1. Prefrontal (Top Front of the eye)
2. Post-orbital (Top back of the eye)
3. Jugal (Bottom back of the eye)
4. Lacrimal (Bottom front of the eye)

Question 16

What are the Three Temporal series in the dermal skull elements in primitive tetrapods?

Answer 16

Behind the orbital series (from most cranial to caudal?)

1. Intertemporal
2. Supratemporal
3. Tabular

These bones are usually lost to form the temporal bone

Question 17

What are the three other series across the bottom of the dermal skull elements in primitive tetrapods?

Answer 17

From front to back

1. Dentary
2. Splenial
3. Angular

Question 18

What are the two Cheek series in the dermal skull elements in primitive tetrapods?

Answer 18

From Front to back behind the maxillary bone

1. Quadratojugal
2. Squamousal

Notes: The squamosal often forms the squamous part of the temporal bone

The quadratojugal may form part of the zygomatic arch.

Question 19

What are the two tooth-bearing lateral series of dermal bones in the primitive tetrapod skull?

Answer 19

Forms the margins of the upper jaw

1. Far front is the Premaxillary bone
2. Followed by the maxillary bone.

Question 20

What portions of the primitive tetrapod skull remain conserved in modern mammals?

Answer 20

1. Dentary
2. Maxillary
3. Lacrimal
4. Nasal
5. Jugal
6. Squamous

Question 21

List 6 generalizations about the reptilian skull

Answer 21

1. Reptilian skull, including the chonrocranium, is well ossified.
2. Primitive forms had boxlike skulls, but modern forms have developed arches and openings
3. Elements of dermatocranium are reduced in modern forms.
4. Many of the reptilian dermal bones are homologous with mammal skulls.
5. Single median occipital condyle.
6. 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.

Question 22

Compare the reptilian skull arches and openings between anapsids and diapsids

Answer 22

• 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.

Question 23

Compare the reptilian openings and arches between a euryapsid and a synapsid

Answer 23

• 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.

Question 24

What is one unique thing about the skull of anapsids?

Answer 24

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.

Question 25

What type of reptilian skull did mammals retain?

Answer 25

Synapsid

Question 26

Describe the jaw articulation in tetrapods.

Answer 26

• Jaw articulation in reptiles and amphibians is between the articular and the quadrate.
• = Autosylic
• The articular is derived from the proximal end of Meckel’s cartilage (first branchial arch).
• The quadrate is derived from the proximal end of the palatopterygoquadrate cartilage (first branchial arch).
• • The hyomandibular is no longer needed to brace the upper jaw against the braincase.
• • The hyomandibular forms the columella (the stapes forms from the proximal portion).
• • The stapes extends from the tympanic membrane to the fenestra ovalis (opening into the inner ear chamber.
• Note: Both amphibian and reptile skulls are autostylic

Question 27

Describe the development of the braincase in pelycosaurs (mammal-like reptiles)

Answer 27

• In pelycosaurs the basisphenoid is formed from the parachordal cartilages and is not fused to the epiterygoids, which are ossifications from the PPQB.
• The epipterygoids form a movable basal articulation with the braincase and each sends a rod-like process up towards the skull roof.
• The epipterygoids do not extend to the dermal roofing bones of the cranial cavity.
• Floor of braincase = Basisphenoid (BS)
• Not fused to epipterygoids (EP).
• Epipterygoids do not extend to dermal roof.

Question 28

Describe the development of the braincase floor in therapsids

Answer 28

• In therapsids the basisphenoid is fused to the epipterygoids and the pterygoids (dermal bones).
• The epipterygoids still do not extend to the dermal roofing bones.
• Basisphenoids fused to epipterygoids and pterygoids.
• Epipterygoids do not extend to dermal roof.

Question 29

Describe the development of the braincase floor in mammals

Answer 29

• In mammals, the basisphenoid (BS) (braincase floor) is fused with both the epipterygoids and the pterygoids.
• The epipterygoids (EP) extend up to and fuse with the dermal roofing bones.
• The pterygoids (PT) (dermal bones) form the pterygoid plates in the mammalian skull which serve as sites for muscles involved in jaw movement
• Basisphenoids fused to epipterygoids and pterygoids.
• Epipterygoids extend to dermal roof.

Question 30

Describe the development of the secondary palate

Answer 30

• Primary palate = floor of braincase.
• Secondary palate formed from:
• Premaxillae
• Maxillae
• Palatines
• Secondary Palate Function: Separates food stream from air stream.
• Especially important in homeotherms
• Found in: Crocodilians, Therapsids, Mammals.

Question 31

Describe the mammalian skull

Answer 31

• Synapsid type of skull
• Zygomatic arch:
• From jugal and squamosal bones
• Loses some dermal elements.
• Development of crests for muscle attachment:
• Sagittal crest
• Nuchal (neck) crest
• Secondary palate
• Jaw articulation:
• Craniostylic:
• • Between dentary and temporal bones
• • Quadrate becomes incus
• • Articular becomes malleus
• Mandible develops as two bones that fuse together, but some non-primates have mandibles that remain separate.

Question 32

What is the ethmoid

Answer 32

A square bone at the root of the nose, forming part of the cranium, and having many perforations through which the olfactory nerves pass to the nose.

Question 33

I can’t tell if the ethmoid is the same is the cribriform plate. But if it is, describe the components of the ethmoid.

Answer 33

• Cribriform plate
• Crista galli: Attachment for falx cerebri
• Perpendicular plate
• Labyrinth: Superior and middle nasal conchae
• Ethmoid air cells

Question 34

What separates the boundaries of the temporal region?

Answer 34

• Superior and posterior boundary: Inferior temporal line
• Anterior boundary: Frontal process of zygomatic
• Inferior: Zygomatic arch
• Floor: Greater wing of sphenoid, Squamous temporal, frontal, and parietal

Question 35

What are the contents of the temporal region?

Answer 35

• Temporalis muscle
• Deep temporal nerve and arteries
• Zygomaticus nerve

Question 36

There are two main “lines” running along the temporal region

What is connected by the superior (Higher) line and the inferior (lower line)?

Answer 36

• Superior: For attachment of temporalis fascia.

- Inferior: For attachment of temporalis muscle.

Question 37

Describe the Muscles of Mastication

Answer 37

• All innervated by mandibular branch of CN V.
• Masseter:
• Zygomatic bone to lateral surface of ramus and coronoid process
• Elevates and protracts mandible
• Temporalis:
• Temporal fossa and fascia to coronoid process
• Elevates and retracts mandible
• Lateral pterygoid:
• Lateral pterygoid plate and sphenoid to front of mandible and TMJ
• Protracts mandible; depresses chin (bilateral; grinding (unilateral) * Medial pterygoid:
• Lateral pterygoid plate and maxilla to medial surface of mandible near angle
• Elevates, protracts, grinding (unilateral)
• Too lazy to make a flashcard for it, but see slide 52 for location of these muscles.

Question 38

Describe the synovial joint located in the temporomandibular joint

Answer 38

• Between head of mandible (condyloid process) and mandibular fossa of temporal bone
• Intervening cartilage: Divides joint into superior and inferior compartments. Allows mandible to protract and retract as well as elevate and depress

Question 39

Describe the ligaments of the temporomandibular joint

Answer 39

• Temporomandibular ligament:
• Base of zygomatic process to mandibular neck
• Stylomandibular ligament:
• Styloid process to angle of mandible
• Runs between parotid and submandibular glands
• Sphenomandibular ligament:
• Sphenoid spine to mandibular lingula
• Lies medial to TMJ