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SKELETAL SYSTEM: SKULL & VISCERAL SKELETON

SKELETAL SYSTEM: SKULL & VISCERAL SKELETON. Mrs. Ofelia Solano Saludar Department of Natural Sciences University of St. La Salle Bacolod City. The vertebrate skull consists of:.

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SKELETAL SYSTEM: SKULL & VISCERAL SKELETON

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  1. SKELETAL SYSTEM: SKULL & VISCERAL SKELETON Mrs. Ofelia Solano Saludar Department of Natural Sciences University of St. La Salle Bacolod City

  2. The vertebrate skull consists of: Neurocranium(also called endocranium, chondrocranium or primary braincase) Dermatocranium(membrane or dermal bones) Splanchnocranium(visceral skeleton)

  3. 1. CHONDROCRANIUM or NEUROCRANIUM • Cartilaginous stage protects the brain • Begins as a pair of parachordal cartilages alongside the notochord (derived from sclerotome), and the prechordal cartilages or trabeculaecranii(derived from neural crests) anterior to these.

  4. Cartilages derived from neural crest also appears in the: olfactorycapsulespartially surrounding the nasal epithelium, oticcapsule surrounding the inner ear, orbital/ opticcapsulesaround the eyes

  5. Completion of floor, walls, & roof: • Parachordalsjoin the notochord and expand to form the basal plate, floor of hindbrain, occipital condyles (1-2), and foramen magnum • Ethmoidplate – prechordals fuse with olfactory capsules; optic capsules remain independent

  6. Basal plate - fuses with otic capsules • Development of cartilaginous walls (sides of braincase) and a cartilaginous roof over the brain in cartilaginous fishes • Foramina remain for nerves & blood vessels • Hypophysealfenestraremains for pituitary gland and carotid arteries

  7. Cartilaginous fishes- retain a cartilaginous neurocranium throughout life; completes skull by forming a cartilaginous roof (tectum) over neurocranium

  8. Bony fishes, lungfishes, & most ganoids- retain highly cartilaginous neurocranium that is covered by membrane bone Cyclostomes- the cartilaginous components of the embryonic neurocranium remain in adults as independent cartilages

  9. Reptiles: Embryonic Development of Lizard Chondrocranium: Parachordaland trabecular cartilages grow up around brain and sense organs

  10. 2. DERMATOCRANIUM • Consists of membrane bones that encase the chondrocranium and jaws. • Formed a complete roof for the skull of extinct tetrapods, but became reduced in number through loss. • Vacuities also tend to arise in the posterior part of the roof, and these temporal fossae are of importance in the evolution of the various amniotes.

  11. Temporal fossae(plus mammalian zygomatic arch) provide space and surfaces in advantageous positions for accommodating the large powerful muscles (adductor, masseter, temporalis) that operate the lower jaw of amniotes.

  12. Differentiation of synapsid adductor mandibulae into temporalis, superficial masseter, and deep masseter, opposed along the jaw by the pterygoideus

  13. Thedermatocranium lies superficial to the neurocranium& forms the bones of: • Roof of the brain: nasals, frontals, parietals, post- parietals • Posterior angle of skull: intertemporal, supratemporal, tabular, squamosal, quadratojugal • Around orbits: lacrimal, prefrontal, postfrontal, jugal(infraorbital), postorbital • The upper jaw: premaxilla, maxilla

  14. The lower jaw: splenial, postsplenial, angular (tympanic bulla), surangular, prearticular (anterior malleus in mammals), coronoids, dentary • The palate: para- sphenoids, vomer palatines, pterygoids, ectopterygoids (cover palato- quadrate) • The operculum in fishes

  15. PALATAL BONES– the primary palate is the floor on which the brain rests, & the roof of the oral cavity in fishes & amphibians; remain cartilaginous in sharks. • Birds, mammals, some reptiles: • Asecondary palate (plus a soft palate in mammals) develops from processes of the premaxillae, maxillae, and palatines, creating a horizontal partition that separates the oral cavity into nasal & oral passages • Allows chewing and breathing simultaneously • Parasphenoidis lost and internal nares is displaced caudad when palate forms

  16. Evolution of the mammalian bony palate: dermal bones of the margin of the oral cavity expand medially to house nasal passages from external nares to choanae.

  17. 3. SPLANCHNOCRANIUM • Cartilage blastema origin is neural crest • Consists of typically 7 gill or skeletal visceral/ branchial arches • 1st MANDIBULAR ARCH • Dorsal half forms the primitive upper jaw, the palatoquadrateorpterygoquadrate • Lower half forms the lower jaw, the Meckel’scartilage • The upper jaw becomes incorporated into the skull, while the lower jaw forms a movable joint with it.

  18. PALATOQUADRATE CARTILAGES: • Unossifiedin tetrapods, function is taken over by dermal bones • Ossifications occur only in the ascending process (epipterygoid bone), and in the otic process (quadrate bone) which becomes an immovable part of auditory region (except in streptostylic conditions which permits wide gape for swallowing large prey) • MECKEL’S CARTILAGES: • Anterior mentomeckelian bone of amphibians • At the rear is the articular bone which articulates with the quadrate bone of the upper jaw (autostylic suspension)

  19. 2nd HYOID ARCH and other gill arches: • Composed of dorsal paired hyomandibular cartilages, and lateral gill-bearing ceratohyalsof elasmobranchs. • The remainder and the other 5 arches contribute to the hyoid apparatus and laryngeal cartilages of tetrapods. • Operculum is the fold of the hyoid arch that extends over the gill slits in holocephalans& bony fishes; in tetrapodsno vestiges of opercular bones remain

  20. HYOID CARTILAGES • Hyomandibular cartilage ossifies to form hyomandibulaof fishes and suspend lower jaw (hyostylic suspension); in tetrapods, it gives rise partly to the columellaof the ear • Remainder of hyoid arch fuse with gill arches to form hyobranchial skeleton consisting of: • Hyoid apparatus - serves as support for tongue and larynx, muscle attachment, buccal respiration of amphibians • Laryngeal cartilages- support voice box chamber

  21. 3. FORMATION OF THE COMPLETE SKULL • CENTERS OF OSSIFICATION appear which converts the chondrocranium into a complete skull that consists of: • Cartilage bones ossified in the chondrocranium, sense capsules, hyoid and mandibulararches • Dermal bones covering the cartilage bones everywhere except on midventral surface and posterior end of the skull. • Degree of ossification is greater in higher members of each group; cartilaginous skulls result from retrogressive processes.

  22. OCCIPITAL CENTERS Occipital group: encircling the foramen magnum are the: basioccipital, exoccipital (2), supraoccipital In mammals, all 4 occipital elements typically fuse to form a single occipital bone surrounding the foramen magnum

  23. Occipital condyles are projections by which the skull articulates with the atlas. • Fishes and primitive tetra- pods have only 1 condyle formed by basioccipital and partly by exoccipital. • 2 condyles present in amphibians and mammals result from reduction of basioccipital and enlargement of exoccipital.

  24. SPHENOID CENTERS • Posterior sphenoid group: basisphenoid, pleurosphenoid (not the mammalian alisphenoid, epipterygoid location) • Orbitosphenethmoid region: presphenoid, orbitosphenoids, mesethmoid. • In mammals, the basicranialaxis is occupied by: basioccipital, basisphenoid, presphenoid, mesethmoid (absent in some)

  25. ETHMOID CENTERS • Remain cartilaginous & form anterior to sphenoid • In most mammals, the nasal chamber is large & filled with ridges from the ethmoid bones called the turbinals or ethmoturbinals. • These bones are covered with olfactory epithelium in life and serve to increase the surface area for a more acute sense of smell (olfaction). • Another ethmoid bone, the cribriform plate, separates the nasal chamber from the brain cavity within the skull.

  26. SENSE CAPSULES: • OTIC - the cartilaginous otic capsule is replaced in lower vertebrates by several bones: prootic, opisthotic, epiotic, pterotic, sphenotic • One or more of these may unite with adjacent replacement or membrane bones: • Frogs & most reptiles - opisthotics fuse with exoccipitals • Birds & mammals - prootic, opisthotic, & epiotic unite to form a single petrosal (periotic or petromastoid) bone; the petrosal, in turn, sometimes fuses with the squamosal to form the temporal bone • OPTIC– gives rise to sclerotic bones around pupil of reptiles and birds (absent in mammals)

  27. blue- chondrocranium; pink-dermatocranium; yellow- splanchnocranium

  28. JAW SUSPENSIONS • Autostyly (left) - hyomandibula has no role in bracing the jaws (lungfish & tetrapods) • Amphistyly(middle) - jaws & hyomandibula both braced directly against the braincase (extinct sharks) • Hyostyly(right) - mandibular cartilage is braced against the otic capsule; jaws braced against hyomandibula (sharks&present day bony fishes)

  29. PHYLOGENY OF THE VERTEBRATE SKULL PLACODERMS

  30. CROSSOPTERYGIANS- the dermatocranium forms a series of paired and unpaired bones along mid-dorsal line of skull LABYRINTHODONTS- theseunpaired bones are lost but a series of paired bones resulted (nasals, frontals, parietals, & dermoccipitals)

  31. AGNATHA • Chondrocranium: remains cartilaginous throughout life; skull roof is fibrous and protects brain & sensory structures • Splanchnocranium: no ancestral branchial skeleton; lingual cartilage bears horny teeth; continuous basket with branchialfunction • Dermatocranium: no dermal armor

  32. CHONDRICTHYES Chondrocranium: calcified; with 2 occipital condyles and foramen magnum; otic and nasal capsules fused to neurocranium

  33. Splanchnocranium: mandibular arch gives rise to palatoquadrate and Meckel’s cartilages; hyoid arch composed of hyomandibula, ceratohyal, basihyal cartilages

  34. TELEOSTS • Neurocranium: remain cartilaginous in chondrosteans, neopterygians, dipnoans; ossifies via the four ossification centers in most fishes • Dermatocranium: numerous dermal bones overlying neurocranium • Splanchnocranium: resembles that of sharks except that bone is added; anterior part of palatoquadrateensheathed by dermal maxilla and premaxilla bones

  35. Caudal ends undergo endochondral ossification & become the quadrate bone; the remainder becomes the palatine & pterygoid bones. • Caudal part of Meckel’s cartilage ossifies as articular bones; remainder becomes invested by dentary and angular membrane bones • Hyomandibulaossifies to become symplectic and interhyal bones • Moveable bony operculum • Hyostylic suspension (ray-finned fish); Autostylic suspension (Dipnoans); Amphistylic suspension (Crossopterygians)

  36. AMPHIBIANS • Neurocranium: remains cartilaginous except for sphenethmoid, prootics, exoccipitals • Dermatocranium incomplete (lacrimals and prefrontals only) • lacks temporal region • 2 occipital condyles • Splanchnocranium: larval stages have fish-like gills supported by gill arches • forms altered primary palate with large vacuities to allow retraction of eyeballs

  37. Jaw suspension: Quadrate of upper jaw articulates with articular of lower jaw (autostylic suspension) • Hyomandibulais no longer needed since the jaw has an autostylicsuspension • It is freed up and becomes a rudimentary stapes called the columella

  38. The rest of the hyoid arch plus arches III and IV become the hyoid apparatus for tongue support • Visceral arch V is no longer needed and becomes the new larynx; arches VI and VII are absent

  39. REPTILES • Neurocranium: • Well ossified, with fewer bones, and single occipital condyle • Dermatocranium: • Many bones, but fewer than bony fish; crocodilians retain the largest number • In many lizards, a parietal foramen houses a median eye

  40. Splanchnocranium: • Similar to amphibians; snakes have vestigial branchial skeleton • Stapes – functional columella • Hyoid apparatus: larynx • Quadrate-articularjoint forms autostylicsuspension; forms part of the kinetic mechanism of the skull • The hyoid consists of a body and 2 or 3 horns (cornua) in the pharyngeal walls. • The entoglossus, a long bony process extends from the hyoid body forward into a long darting tongue (snakes, lizards, birds).

  41. EARLY TETRAPOD SKULL top: dermatochraniumremoved red: dermatocranium; blue: chondrocranium; green: splanchnocranium

  42. Formation of partial or complete secondary palate • Development of temporal fossae bounded by arches: infratemporal arch (below ventral fossa); zygomatic arch (infratemporal arch); supratemporal arch (below dorsal fossa)

  43. CRANIAL KINESIS • Independent movement of one or more skull bones, especially between the upper jaw and braincase; e.g., a pivoting quadrate • Results from reduction or loss of arches along with presence of intracranial joints • Advantages: • provides a way to change the size and configuration of the mouth rapidly • optimize biting and rapid feeding • Disadvantages: lose force, hard to optimize apposition of occlusive surfaces

  44. These fossae and arches provide room for huge chewing muscles which allows rotary chewing

  45. BIRDS • Neurocranium- thin, highly vaulted or domed, but basically a reptile skull • Dermatocranium: • Modified diapsid: supratemporal arch is lost, one big opening confluent with orbit • Beak instead of teeth; premaxilla & dentary elongated • Splanchnocranium- similar to reptiles • Pivoting quadrates allow cranial kinesis although ectopterygoids are absent, and immobile parasphenoid is fused to basisphenoid. • When quadrate is pushed forward, the motion is transmitted to upper beak via a movable palate, a movable zygomatic arch, or both.

  46. MAMMALS • Neurocranium: • Larger, fewer bones due to fusion; sutures found between skull bones • Skull increasingly domed as cerebral hemispheres increase is size • Neurocranium is incomplete dorsally, resulting to fontanels (a bregmatic bone ossifies and forms an anomaly in human skulls) • Petrosal (periotic) bones form in the otic capsules • 2 occipital condyles

  47. Dermatocranium: • Decreased number of bones • Synapsid skull; zygomatic arch varies from massive to slender, even incomplete in insectivores • Air-filled cranial sinuses: frontals sinuses extend into horns; sinusitis is a common aliment in humans • Present in Homo erectus and Mongolians, is a postparietal or Inca bone

  48. Temporal complex has intramembranous and endochondral origin: • Squamousportion- squamosal of lower tetrapods • Tympanic bulla- unique to mammals and encloses the middle ear; tympanic bone surrounds the eardrum, entotympanic bone represents the bulla • Petrousportion- ossified otic capsule • Mastoid portion- new in mammals; dorsal part of hyoid arch may fuse to mastoid to form styloid process • Tympanic and petrous portions unite to form petrotympanic bone

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