1. Mrs. Ofelia Solano Saludar
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 trabeculae cranii (derived from neural crests) anterior to these.

4. Cartilages derived from neural crest also appears in the:
olfactory capsules partially surrounding the nasal epithelium,
otic capsule surrounding the inner ear,
orbital/ optic capsules around the eyes

5. Completion of floor, walls, & roof:
Parachordals join the notochord and expand to form the basal plate, floor of hindbrain, occipital condyles (1-2), and foramen magnum
Ethmoid plate – 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
Hypophyseal fenestra remains 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: Parachordal and 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.

12. 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.

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

14. The dermatocranium 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

15. 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

16. 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:
A secondary 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
Parasphenoid is lost and internal nares is displaced caudad when palate forms

17. 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.

18. 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 palatoquadrate or pterygoquadrate
Lower half forms the lower jaw, the Meckel’s cartilage
The upper jaw becomes incorporated into the skull, while the lower jaw forms a movable joint with it.

19. PALATOQUADRATE CARTILAGES:
Unossified in 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)

20. 2nd HYOID ARCH and other gill arches:
Composed of dorsal paired hyomandibular cartilages, and lateral gill-bearing ceratohyals of 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 tetrapods no vestiges of opercular bones remain

21. HYOID CARTILAGES
Hyomandibular cartilage ossifies to form hyomandibula of fishes and suspend lower jaw (hyostylic suspension); in tetrapods, it gives rise partly to the columella of 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

22. 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 mandibular arches
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.

23. 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

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

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

26. 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.

27. 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)

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

29. 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)

30. PHYLOGENY OF THE VERTEBRATE SKULL
PLACODERMS

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

32. 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 branchial function
Dermatocranium: no dermal armor

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

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

35. 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 palatoquadrate ensheathed by dermal maxilla and premaxilla bones

36. 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
Hyomandibula ossifies to become symplectic and interhyal bones
Moveable bony operculum
Hyostylic suspension (ray-finned fish); Autostylic suspension (Dipnoans); Amphistylic suspension (Crossopterygians)

37. 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

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

39. 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

40. 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

41. Splanchnocranium:
Similar to amphibians; snakes have vestigial branchial skeleton
Stapes – functional columella
Hyoid apparatus: larynx
Quadrate-articular joint forms autostylic suspension; 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).

42. top: dermatochranium removed
EARLY TETRAPOD SKULL
top: dermatochranium removed
red: dermatocranium; blue: chondrocranium; green: splanchnocranium

43. 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)

44. 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

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

47. 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.

48. 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

49. 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

50. Temporal complex has intramembranous and endochondral origin:
Squamous portion- squamosal of lower tetrapods
Tympanic bulla- unique to mammals and encloses the middle ear; tympanic bone surrounds the eardrum, entotympanic bone represents the bulla
Petrous portion- 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

51. Squamosal
Otic capsule
Mastoid
Tympanic bulla

52. Pterygoids become reduced as winglike processes of the sphenoid
3 pairs of turbinal bones (nasal conchae) develop in the nasal passageways: superior concha is covered with olfactory epithelium; the 2 lower conchae are covered by nasal epithelium with venous plexuses that warm the air en route to the lungs

53. Squamosal articulates with dentary bone, which is sole lower jaw bone

54. Splanchnocranium: unossified tips of palato-quadrate and Meckelian cartilages give rise to middle ear ossicles, along with the columella:
quadrate becomes incus
articular becomes part of malleus
hyomandibula has already became stapes

57. Hyoid apparatus and larynx:
Consists of a body & 2 or 3 horns (cornua);
Anchors tongue, provides Attachment for some extrinsic muscles of larynx
Site of attachment of muscles that aid in swallowing

58. In addition to cricoid and arytenoid cartilages common to tetrapods, mammals have thyroid cartilages arising from the 4th and 5th arches

59. ARCH
SHARK
TELEOST
FROG
REPTILE
MAMMAL 1
Palatoquadrate
Meckel’s
cartilage
Quadrate
Epipterygoid
Metapterygoid
Articular
Ammulus tympanicus
Mentomeckelian
Incus
Alisphenoid
Malleus 2
Hyomandibula
Ceratohyal
Basihyal
Symplectic
Interhyal
Epihyal
Hypohyal
Columella (stapes)
Anterior horn of hyoid
Body of hyoid
Entoglossus
Styloid process 3
Pharyngobranchial
Epibranchial
Ceratobranchial
Hypobranchial
2nd horn of hyoid 4
Branchial skeleton
Last horn of hyoid
Thyroid cartilages 5
Cricoid and arytenoids 6
Not present 7

60. EVOLUTIONARY CHANGES IN MAMMALIAN SKULL:
Loss of connection between head and pectoral girdle to create neck in primitive tetrapods
Increasing skull strength through simplification by loss of bones and articulations
Braincase evolution reflecting enlarged brain
Changes in sense organs (e.g., in median pineal-parietal eye complex and loss of pineal foramen)
Development of secondary palate and respiratory passages
Temporal fenestration and jaw adductor differentiation
Change from quadrate-articular to dentary-squamosal jaw joint with concomitant development of three middle ear bones

61. Homologies among bones are difficult to establish
Sagittal section through skull of ancestral amniote and mammal to show evolution of bones that form braincase; note that the epipterygoid of the primitive amniote splanchnocranium is homologous with alisphenoid in mammals.

62. REGIONAL SERIES OF DERMATOCRANIAL BONES IN EARLY TETRAPOD

63. DERMAL ROOF BONES LOST IN MAMMALS: Circumorbital series: prefrontal, postfrontal, postorbital
Temporal series: intertemporal, supratemporal, tabular (?)
Cheek series: quadratojugal
Lower Jaw: splenials, surangular, coronoids

64. TEETH: teeth of vertebrates are homologous to the placoid scale of elasmobranchs.
Usually of simple form and all alike among lower tetrapods, they become heterodont (several kinds), and thecodont (set in sockets in jaw bones).
Borne in lower tetrapods on various jaw and palatal bones, they become limited in higher ones to the jaw margins.
Teeth of mammals: incisors, canines, premolars, molars; juvenile (no molars), and permanent sets
Trituberculate theory of mammalian tooth origin: 2 cusps arising from a ridge (cingulum) from neck of tooth are added to simple reptilian tooth. Teeth of upper jaw are slightly behind those of lower jaw.

65. HUMAN AND ANTHROPOID APE SKULL:
large, rounded cranial portion
flattened facial portion, vertical orientation
complete separation of the orbits from the temporal fossae
reduction of the nasal cavities and turbinals
large mastoid process
absence of a tympanic bulla
extensive fusions of the skull bones
unspecialized teeth: 2 incisors, slightly enlarged canines, bunodont (separated rounded cusp) molars

67. Name the bones of the neurocranium of a basal craniate, and their fused derivatives.
What major steps occurred in the phylogenetic development of the “complete” cranium?
Tabulate: regions of ossification in the cranium, and the bones present in each region of the teleost, amphibian, reptilian, and mammalian skulls.
Tabulate: pharyngeal arches of basal vertebrate, and their homologues in teleost, amphibians, reptiles, mammals
Tabulate: dermal bones in each of these regions of the teleost, amphibian, reptilian, mammalian skull: roof, upper and lower jaw, palate
Describe the phylogenetic patterns for the craniate temporal fossae, and their fuctional role in each group.
Name the bones that contribute to the formation of the primary and secondary palate.
List the types of jaw suspension, and their participating bones.
Discuss the phylogeny of the mammalian middle ear bones.
What is the functional significance of cranial kinesis?

68. THE APPENDICULAR SKELETON
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THE APPENDICULAR SKELETON