Lecture 10 Flashcards
(37 cards)
Generalizations of Reptilian Skull
- well ossified
- modern forms have developed arches and openings (primitive more boxlike)
- elements of dermatocranium are reduced in modern forms
- many 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 skill for muscle attachment and the development of the openings and arches
Anapsid Skull
- no arches and no additional openings
- found in cotylosaurs and turtles
Diapsid skull
- both lateral and dorsolateral openings
- two arches
- found in most reptiles
- both arches are present in Sphenodon
- lizards have lost the lower arch
- snakes have lost both bars
- this frees the quad rate and allows for a more movable lower jaw to give them more mobility
Euryapsid (Parapsid) Skull
- may be variant of a Diapsid skull
- single dorsolateral opening bounded inferiority by postorbital and squamousal bones
- found in plesiosaurs and icthyosaurs
Synapsid skull
- found in mammal-like reptiles and mammals
- single opening bounded inferiority by the zygomatic arch
Vertebrate skull in Sharks, Skates, and Rays
Formed entirely of cartilage; failure to replace cartilage with bone in the adult is an example of neoteny
Vertebrate skull organization
Composed of the chondrocranium and dermatocranium
Chondrocranium
Neurocranium:
-aka the brain case
Splanchnocranium:
-aka pharyngeal gill arches
Neurocranium
- Braincase
- cartilage and/or endochondral bone
- Includes three pairs of cartilaginous capsules housing special sensory organs:
- Olfactory (most anterior)
- Optic
- Otic (most posterior) - floor forms two pairs of cartilaginous plates
- Parachordals
- Prechordals - posterior wall
- roof
Endochondral ossifications of neurocranium
Basioccipital:
- Below foramen magnum
Exoccipital:
- Paired lateral to foramen
Supraoccipital:
- Above foramen magnum
Basisphenoid (and presphenoid)
Splanchnocranium
Six pairs of cartilaginous or bony arches:
- 1st arch
-Mandibular arch:
Dorsal part= palatopterygoquadrate bar
-ossifications=epipterygoids
Ventral part= Meckel's cartilage
-ossifications=quadrate and articular -2nd arch
-Hyoid arch
In many fishes, it braces the palatopterygoquadrate bar against the brain case
Types of jaw suspension in fishes
Hyostylic and Autostylic
Hyostylic Jaw Suspension
-hyoid braces upper jaw against neurocranium
Examples: Elasmobranchs, holosteans, teleosts, and dipnoans
Autostylic Jaw Suspension
- upper jaw is fused to Braincase
- jaw articulation is between quadrate and articular
Example: chimaeras and lungfishes
Modern Amphibian Skull
- reduction of dermal elements
- retention of considerable cartilage
- paired occipital condyles
- autostylic jaw articulation
Hyomandibular=columella
Dermal skull elements of primitive tetrapod
Roof series:
Nasal
Frontal
Parietal
Postparietal
Circumorbital series:
Prefrontal
Postorbital
Jugal
Lacrimal
Temporal series:
Intertemporal
Supratemporal
Tabular
Cheek series:
Squamosal
Quadratojugal
*^may form part of the zygomatic arch
Lateral tooth-bearing series:
*Forms margins of upper jaw.
Premaxillary
Maxillary bones
Example of neoteny:
Failure to replace cartilage with bone in the adult
Vertebrate skull
Forms the other part of the axial skeleton
- may be formed entirely of cartilage
- may be a combination of cartilage, dermal bone, and/or endochondral bone
In vertebrates, brain case develops in the embryo as an incomplete cartilaginous box with numerous openings (foramina) thru which pass nerves and blood vessels to and from the brain
-additional cartilaginous capsules develop to enclose the special sensory organs such as olfactory apparatus, eyes, and semicircular canals (balance)
Reptilian skull: generalizations
- well ossified
- primitive forms had boxlike skulls, modern have developed arches and openings
- elements of dermatocranium are reduced in modern forms
- many reptilian dermal bones are homologous with mammal skulls
- single median occipital condyle
- jaw musculature well-developed
- related to development of the increase in surface areas on sides of skull for muscle attachment and the development of the openings and a Rachel
Reptilian skull arches and openings: Anapsid
No arches and no additional openings
Found in cotylosaurs and turtles
Reptilian skull arches and openings: Diapsids
Both lateran and dorsolateral openings
2 Arches
Found in most reptiles:
- both arches are present in Sphenodon
- lizards have lost the lower arch
- snakes have lost both bars:
- this frees the quadrate and allows for more movable lower jaw
Reptilian skull arches and openings: Euryapsid (Parapsid)
- May be a variant of a diapsid skull
- Single dorsolateral opening bounded inferiority by postorbital and squamosal bones
- Found in plesiosaurs and icthyosaurs
Reptilian skull arches and openings: Synapsids
- Found in mammal-like reptiles and mammals
- Single opening bounded inferiority by the zygomatic arch
Tetrapod jaw articulation
Jaw articulation is between the articular and quadrate
- Autosylic
- The articular arch 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)
