Mrs. Ofelia Solano Saludar Department of Natural Sciences University of St. La Salle Bacolod City The vertebrate skull consists of: Neurocranium (also called endocranium, chondrocranium or primary braincase) Dermatocranium (membrane or dermal bones) Splanchnocranium (visceral skeleton) 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. Cartilages derived from neural crest also appears in the: 1. olfactory capsules partially surrounding the nasal epithelium, 2. otic capsule surrounding the inner ear, 3. orbital/ optic capsules around the eyes 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 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 Cartilaginous fishes - retain a cartilaginous neurocranium throughout life; completes skull by forming a cartilaginous roof (tectum) over neurocranium 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 Reptiles: Embryonic Development of Lizard Chondrocranium: Parachordal and trabecular cartilages grow up around brain and sense organs 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. 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. Differentiation of synapsid adductor mandibulae into temporalis, superficial masseter, and deep masseter, opposed along the jaw by the pterygoideus The dermatocranium lies superficial to the neurocranium & forms the bones of: Roof of the brain: nasals, frontals, parietals, postparietals Posterior angle of skull: intertemporal, supratemporal, tabular, squamosal, quadratojugal Around orbits: lacrimal, prefrontal, postfrontal, jugal (infraorbital), postorbital The upper jaw: premaxilla, maxilla The lower jaw: splenial, postsplenial, angular (tympanic bulla), surangular, prearticular (anterior malleus in mammals), coronoids, dentary The palate: parasphenoids, vomer palatines, pterygoids, ectopterygoids (cover palatoquadrate) The operculum in fishes 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 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. 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. 1. 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) 2. 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) 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 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 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. 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 Occipital condyles are projections by which the skull articulates with the atlas. Fishes and primitive tetrapods 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. 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) 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. SENSE CAPSULES: 1. 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 2. OPTIC – gives rise to sclerotic bones around pupil of reptiles and birds (absent in mammals) blue- chondrocranium; pink-dermatocranium; yellow- splanchnocranium 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) P L A C O D E R M S CROSSOPTERYGIANS- the dermatocranium forms a series of paired and unpaired bones along middorsal line of skull LABYRINTHODONTS- these unpaired bones are lost but a series of paired bones resulted (nasals, frontals, parietals, & dermoccipitals) 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 CHONDRICTHYES Chondrocranium: calcified; with 2 occipital condyles and foramen magnum; otic and nasal capsules fused to neurocranium Splanchnocranium: mandibular arch gives rise to palatoquadrate and Meckel’s cartilages; hyoid arch composed of hyomandibula, ceratohyal, basihyal cartilages 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 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) AMPHIBIANS Neurocranium: remains cartilaginous except for sphenethmoid, prootics, exoccipitals Dermatocranium incomplete (lacrimals and prefrontals only) o lacks temporal region o 2 occipital condyles Splanchnocranium: larval stages have fish-like gills supported by gill arches o forms altered primary palate with large vacuities to allow retraction of eyeballs 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 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 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 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). EARLY TETRAPOD SKULL top: dermatochranium removed red: dermatocranium; blue: chondrocranium; green: splanchnocranium 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) 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: o provides a way to change the size and configuration of the mouth rapidly o optimize biting and rapid feeding Disadvantages: lose force, hard to optimize apposition of occlusive surfaces These fossae and arches provide room for huge chewing muscles which allows rotary chewing 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. 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 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 Temporal complex has intramembranous and endochondral origin: 1. Squamous portion- squamosal of lower tetrapods 2. Tympanic bulla- unique to mammals and encloses the middle ear; tympanic bone surrounds the eardrum, entotympanic bone represents the bulla 3. Petrous portion- ossified otic capsule 4. 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 Squamosal Mastoid Otic capsule Tympanic bulla 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 Squamosal articulates with dentary bone, which is sole lower jaw bone Splanchnocranium: unossified tips of palatoquadrate 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 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 In addition to cricoid and arytenoid cartilages common to tetrapods, mammals have thyroid cartilages arising from the 4th and 5th arches ARCH SHARK TELEOST FROG REPTILE MAMMAL 1 Palatoquadrate Meckel’s cartilage Quadrate Epipterygoid Metapterygoid Articular Quadrate Ammulus tympanicus Articular Mentomeckeli an Quadrate Epipterygoid Articular Incus Alisphenoid Malleus 2 Hyomandibula Ceratohyal Basihyal Hyomandibula Symplectic Interhyal Epihyal Ceratohyal Hypohyal Basihyal Columella (stapes) Anterior horn of hyoid Body of hyoid Columella (stapes) Anterior horn of hyoid Entoglossus Columella (stapes) Styloid process Body of hyoid 3 Pharyngobranchial Epibranchial Ceratobranchial Hypobranchial Pharyngobranchial Epibranchial Ceratobranchial Hypobranchial Body of hyoid 2nd horn of hyoid Body of hyoid 2nd horn of hyoid Body of hyoid 4 Branchial skeleton Branchial skeleton 2nd horn of hyoid Last horn of hyoid Thyroid cartilages 5 Branchial skeleton Branchial skeleton Cricoid and arytenoids Cricoid and arytenoids Cricoid and arytenoids 6 Branchial skeleton Branchial skeleton Not present Not present Not present 7 Branchial skeleton Branchial skeleton Not present Not present Not present 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 pinealparietal 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 dentarysquamosal jaw joint with concomitant development of three middle ear bones 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. REGIONAL SERIES OF DERMATOCRANIAL BONES IN EARLY TETRAPOD DERMAL ROOF BONES LOST IN MAMMALS: Circumorbital series: prefrontal, postfrontal, postorbital Temporal series: intertemporal, supratemporal, tabular (?) Cheek series: quadratojugal Lower Jaw: splenials, surangular, coronoids 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. 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 1. Name the bones of the neurocranium of a basal craniate, and their fused derivatives. 2. What major steps occurred in the phylogenetic development of the “complete” cranium? 3. Tabulate: regions of ossification in the cranium, and the bones present in each region of the teleost, amphibian, reptilian, and mammalian skulls. 4. Tabulate: pharyngeal arches of basal vertebrate, and their homologues in teleost, amphibians, reptiles, mammals 5. Tabulate: dermal bones in each of these regions of the teleost, amphibian, reptilian, mammalian skull: roof, upper and lower jaw, palate 6. Describe the phylogenetic patterns for the craniate temporal fossae, and their fuctional role in each group. 7. Name the bones that contribute to the formation of the primary and secondary palate. 8. List the types of jaw suspension, and their participating bones. 9. Discuss the phylogeny of the mammalian middle ear bones. 10.What is the functional significance of cranial kinesis?