Skeletal Tissue The Axial Skeleton Human Anatomy Skeletal

Skeletal Tissue & The Axial Skeleton Human Anatomy

Skeletal Tissue, Ch 6

The Skeletal System • Composed of bones, cartilages, & joints that form the internal framework of body -We’ll explore the microscopic & gross structure of the skeletal tissues & system

Cartilage • Location & basic structure – Found throughout adult body • • Ear & epiglottis Articular cartilages & costal cartilage Larynx, trachea, & nose Intervertebral discs, pubic symphysis, & articular discs

Cartilage Epiglottis Cartilage in external ear Cartilages in nose Articular cartilage of a joint Thyroid cartilage Cricoid cartilage Larynx Trachea Lung Costal cartilage Cartilage in intervertebral disc Meniscus (padlike cartilage in knee joint) Articular cartilage of a joint Pubic symphysis Respiratory tube cartilages in neck and thorax Cartilages Hyaline cartilages Elastic cartilages Fibrocartilages

Cartilage • Is surrounded by perichondrium • Consists primarily of water • Resilient tissue it springs back to original shape

Types of Cartilage – Review! • Hyaline cartilage (glassy) – Most abundant cartilage – Provides support through flexibility • Elastic cartilage contains many elastic fibers – Able to tolerate repeated bending • Fibrocartilage resists strong compression & strong tension – An intermediate between hyaline & elastic

Cartilages in the Adult Body (remember these? …) Chondrocyte in a lacuna Matrix Chondrocyte in a lacuna Elastic fibers Lacuna Gelatinous ground substance Perichondrium (a) Hyaline cartilage (180 ) (b) Elastic cartilage (470 ) Chondrocyte in a lacuna Collagen fibers (c) Fibrocartilage (285 )

Growth of Cartilage • Appositional growth – Chondroblasts in surrounding perichondrium produce new cartilage • Interstitial growth – Chondrocytes within cartilage divide & secrete new matrix • Cartilage stops growing when the skeleton stops growing

Tissues in Bone • Bones contain several types of tissues – Dominated by bone CT – Contain nervous tissue & blood – Contain cartilage in articular cartilages – Contain ET lining blood vessels

Function of Bones • Support – provides hard framework • Movement – skeletal muscles use bones as levers • Protection of underlying organs • Mineral storage – reservoir for important minerals Ca 2+ • Blood-cell formation – bone contains red marrow • Energy metabolism – osteoblasts secrete osteocalcin; & yellow marrow stores fat

Bone Tissue • Bone tissue – Organic components cells, fibers, & ground substance – Inorganic components mineral salts that invade bony matrix (calcium phosphate)

Extracellular Matrix • Unique composition of matrix – Gives bone exceptional properties – 35% organic components • Contributes to flexibility & tensile strength – 65% inorganic components • Provide exceptional hardness, resists compression!

Cells in Bone • 3 types of cells in bone produce or maintain bone: – Osteogenic cells stem cells that differentiate into osteoblasts – Osteoblasts actively produce & secrete bone matrix • Bone matrix = osteoid – Osteocytes housed within lacunae, keep bone matrix healthy

Cells in Bone • Osteoclasts – 4 th type of cell – Responsible for resorption of bone – Secrete hydrochloric acid (HCl) & lysosomal enzymes to break down bone – The “Grim Reaper” of bone http: //faculty. une. edu/com/abell/histolab 3. htm

Classification of Bones • Long bones longer than wide; a shaft plus ends • Short bones roughly cube-shaped • Flat bones thin and flattened, usually curved • Irregular bones various shapes, do not fit into other categories

Classification of Bones

Gross Anatomy of Bones • Compact bone dense outer layer of bone • Spongy bone internal network of bone

Structure of a Typical Long Bone • • Diaphysis = “shaft” of a bone Epiphysis = ends of a bone Blood vessels well vascularized Medullary cavity = hollow cavity filled with yellow marrow • Membranes – Periosteum, perforating fibers, & endosteum

Structure of a Long Bone Articular cartilage Proximal epiphysis Compact bone Spongy bone Endosteum Epiphyseal line Endosteum Periosteum Compact bone Medullary cavity (lined by endosteum) Diaphysis Yellow bone marrow Compact bone Periosteum Perforating (Sharpey’s) fibers Nutrient arteries Distal epiphysis

Microscopic Structure of Compact Bone • Compact Bone – Contains passage ways for blood vessels, lymph vessels, & nerves – Osteons long cylindrical structures • Function in support • Structurally – resembles rings of a tree in c. s.

Microscopic Structure of Compact Bone Compact bone Central (Haversian) canal Spongy bone Perforating (Volkmann’s) canal Endosteum lining bony canals and covering trabeculae Osteon (Haversian system) Circumferential lamellae Perforating (Sharpey’s) fibers Lamellae Nerve Vein Artery Canaliculi Osteocyte in a lacuna Lamellae Central canal Lacunae Periosteal blood vessel Periosteum Lamellae Central canal Lacunae Interstitial lamellae Lacuna (with osteocyte)

Microscopic Structure of Compact Bone • Osteons contain: – Lamellae – Central canal – Perforating canals – Canaliculi Interstitial lamellae Lamellae Central canal Lacunae Lacuna (with osteocyte)

Microscopic Structure of Compact Bone Artery with capillaries Structures in the central canal Vein Nerve fiber Lamellae Collagen fibers run in different directions Twisting force

Microscopic Structure of Spongy Bone • Spongy Bone – Is less complex than compact bone – Trabeculae contain layers of lamellae & osteocytes • Are too small to contain osteons (no “tree rings”)

Microscopic Structure of Spongy Bone Marrow space Trabecula Osteocytes Endosteum Osteoblasts

Structure of Short, Irregular, & Flat Bones – Contain bone marrow but no marrow cavity – Diploë = Internal spongy bone of flat bones Spongy bone (diploë) Compact bone Trabeculae

Gross Anatomy of Bones Load here (body weight) • Bone design & stress – Anatomy of a bone reflects stresses – Compression & tension greatest at external surfaces Head of femur Compression here Tension here Point of no stress

Bone Markings • Superficial surfaces of bones reflect stresses on them • 3 broad categories of bone markings: – Projections for muscle attachment – Surfaces that form joints – Depressions & openings

Bone Markings

Bone Development • Ossification (osteogenesis) = bone-tissue formation – Membrane bones formed directly from mesenchyme (during embryonic period) • Intramembranous ossification – Other bones develop initially from hyaline cartilage • Endochondral ossification

Intramembranous Ossification Mesenchymal cell Collagen fiber Ossification center Osteoid Osteoblast Osteoid Osteocyte Newly calcified bone matrix Osteoblast 1 Ossification centers appear in the fibrous connective tissue membrane. • Selected centrally located mesenchymal cells cluster and differentiate into osteoblasts, forming an ossification center. 2 Bone matrix (osteoid) is secreted within the fibrous membrane and calcifies. • Osteoblasts begin to secrete osteoid, which is calcified within a few days. • Trapped osteoblasts become osteocytes.

Intramembranous Ossification Mesenchyme condensing to form the periosteum Trabeculae of woven bone Fibrous periosteum Osteoblast Plate of compact bone Diploë (spongy Blood vessel bone) cavities contain red marrow 4 Lamellar bone replaces woven bone, just 3 Woven bone and periosteum form. • Accumulating osteoid is laid down between embryonic deep to the periosteum. Red marrow appears. • Trabeculae just deep to the periosteum thicken and blood vessels in a random manner. The result is a are later replaced with mature lamellar bone, forming network (instead of lamellae) of trabeculae called compact bone plates. woven bone. • Vascularized mesenchyme condenses on the external • Spongy bone (diploë), consisting of distinct trabeculae, persists internally, and its vascular tissue face of the woven bone and becomes the periosteum. becomes red marrow.

Endochondral Ossification • All bones except some bones of the skull & clavicles • Bones are 1 st modeled in hyaline cartilage • Begins forming late in the 2 nd month of embryonic development • Continues forming until early adulthood

Primary ossification centers in the skeleton of a 12 -week fetus Parietal bone Occipital bone Mandible Clavicle Scapula Frontal bone of skull Radius Ulna Humerus Ribs Vertebra Ilium Tibia Femur

Stages in Endochondral Ossification Month 3 Week 9 Childhood to adolescence Birth Articular cartilage Secondary ossification Spongy bone center Epiphyseal blood vessel Area of deteriorating cartilage matrix Hyaline cartilage Epiphyseal plate cartilage Medullary cavity Spongy bone formation Bone collar Primary ossification center 1 Bone collar forms around hyaline cartilage model. Blood vessel of periosteal bud 2 Cartilage in the center of the diaphysis calcifies and then develops cavities. 3 The periosteal bud invades the internal cavities, and spongy bone begins to form. 4 The diaphysis elongates and a medullary cavity forms as ossification continues. Secondary ossification centers appear in the epiphyses in preparation for stage 5. 5 The epiphyses ossify. When completed, hyaline cartilage remains only in the epiphyseal plates and articular cartilages.

Anatomy of Epiphyseal Growth Areas • In epiphyseal plates of growing bones: – Cartilage is organized for quick, efficient growth – Cartilage cells form tall stacks • Chondroblasts at the top of stacks divide quickly – Pushes the epiphysis away from the diaphysis – As chondrocytes die, osteoblasts replace them & secrete bone matrix lengthens bone

Anatomy of Epiphyseal Growth Areas • Older chondrocytes signal surrounding matrix to calcify • Older chondrocytes then die & disintegrate – Leaves long trabeculae (spicules) of calcified cartilage on diaphysis side – Trabeculae are partly eroded by osteoclasts – Osteoblasts then cover trabeculae with bone tissue – Trabeculae finally eaten away from their tips by osteoclasts

Organization of Cartilage within Epiphyseal Plate of Growing Long Bone Resting zone 1 Proliferation zone Cartilage cells undergo mitosis. 2 Hypertrophic zone Older cartilage cells enlarge. Calcified cartilage spicule Osseous tissue 3 Calcification zone Matrix becomes calcified; cartilage cells die; matrix begins deteriorating. 4 Ossification zone New bone formation is occurring.

Postnatal Growth of Endochondral Bones • During childhood & adolescence: – Bones lengthen entirely by growth of the epiphyseal plates – Cartilage is replaced with bone CT as quickly as it grows – Epiphyseal plate maintains constant thickness – Whole bone lengthens

Hormonal Regulation of Bone Growth • Growth hormone produced by the pituitary gland – Stimulates epiphyseal plates (lengthens bones) • Thyroid hormone ensures that the skeleton retains proper proportions • Sex hormones (estrogen & testosterone) – Promote bone growth – But also later induces closure of epiphyseal plates (~stop growing shortly after puberty!)

Postnatal Growth of Endochondral Bones • As adolescence draws to an end: – Chondroblasts divide less often – Epiphyseal plates become thinner • Cartilage stops growing • Replaced by bone tissue no more addition – Long bones stop lengthening when diaphysis & epiphysis fuse

Postnatal Growth of Endochondral Bones • Growing bones widen as they lengthen – Osteoblasts add bone tissue to the external surface of the diaphysis – Osteoclasts remove bone from the internal surface of the diaphysis • Appositional growth of a bone by addition of bone tissue to its surface

Bone Remodeling • Bone is dynamic living tissue – 500 mg of calcium may enter or leave the adult skeleton each day!!! – Some bone of the skeleton is replaced every 3 – 4 years – Compact bone is replaced every 10 years

Bone Remodeling • Bone deposit & removal – Occurs at periosteal & endosteal surfaces • Bone remodeling – Bone deposition accomplished by osteoblasts – Bone reabsorption accomplished by osteoclasts

Osteoclast: A Bone-Degrading Cell • A giant cell with many nuclei • Crawls along bone surfaces • Breaks down bone tissue (reabsorption) – Secretes concentrated HCl – Lysosomal enzymes are released – Derived from blood stem cells Bone matrix Osteocyte within a lacuna Ruffled border of osteoclast Nuclei

Injuries to Bone: Common Types of Fractures

Common Types of Fractures

Common Types of Fractures

Stages of Healing a Fracture Hematoma A hematoma forms. Bony callus of spongy bone New blood vessels Internal callus (fibrous tissue and cartilage) 1 External callus Healed fracture Spongy bone trabecula 2 Fibrocartilaginous callus forms. 3 Bony callus forms. 4 Bone remodeling occurs.

Disorders of Bones • Osteoporosis – Characterized by low bone mass • Bone reabsorption outpaces bone deposition • Occurs most often in women after menopause (no/low estrogen!) • Also aging men (with low T)

Osteoporosis

Disorders of Bones • Osteomalacia – Occurs in adults bones are inadequately mineralized (not enough Ca 2+ & phosphorus) • Rickets – – – Occurs in children analogous to osteomalacia Vit D/Ca 2+/P deficiency not enough Ca 2+ absorbed Bones are brittle, weak, deteriorate Common in industrial Europe (little sunlight) Now in most countries milk, etc. fortified w/ Vit D But Rickets on the rise in U. S. & many countries

Disorders of Bones • Paget’s disease – Characterized by excessive rate of bone deposition enlarged & deformed bones, can lead to pain, arthritis, deformities, fractures, & other complications – Prevalence 1 -8% ( > 40 yrs old) • Osteosarcoma – Most common form of bone cancer – Occurs mainly at the ends of long bones – ~68% survival rates

The Skeleton Throughout Life • Cartilage grows quickly in youth • Skeleton has fewer chondrocytes in the elderly • Bones are a timetable – Mesoderm • Gives rise to embryonic mesenchyme cells – Mesenchyme • Produces membranes & cartilage – Membranes & cartilage ossify (harden) – New bone is added during childhood & youth

The Skeleton Throughout Life • Skeleton grows until age ~18– 21 years • In children & adolescents: bone formation exceeds rate of resorption • In young adults: bone formation & resorption are in balance • In old age: resorption predominates • Bone mass declines with age Healthy diet, moderate sunlight, & exercise can help keep your bones in better shape as you age!

The Axial Skeleton, Ch 7 (also to be used as Lab Guide)

The Skeleton • Consists of: – Bones, cartilage, joints, & ligaments • Composed of 206 bones grouped into 2 divisions: – Axial skeleton (80 bones) – Appendicular skeleton (126 bones)

Axial Skeleton Skull • Formed from 80 named bones • Consists of skull, vertebral column, & bony thorax Thoracic cage (ribs and sternum) Vertebral column Sacrum Cranium Facial bones Clavicle Scapula Sternum Rib Humerus Vertebra Radius Ulna Carpals Phalanges Metacarpals Femur Patella Tibia Fibula (a) Anterior view Tarsals Metatarsals Phalanges

Axial Skeleton Cranium Clavicle Scapula Rib Humerus Vertebra Radius Ulna Bones of pelvic girdle Bones of pectoral girdle Upper limb Carpals Phalanges Metacarpals Femur Tibia Fibula (b) Posterior view Lower limb

The Skull – Cranial & Facial Bones • Facial bones serve to: – Form framework of face – Form cavities for the sense organs of sight, taste, & smell – Provide openings for passage of air & food – Hold the teeth in place – Anchor muscles of face

Facial Bones • Unpaired bones – Mandible & vomer • Paired bones – Maxillae – Zygomatic bones – Nasal bones – Lacrimal bones – Palatine bones – Inferior nasal conchae

Facial Bones Frontal bone Parietal bone Glabella Squamous part of frontal bone Frontonasal suture Supraorbital foramen (notch) Nasal bone Sphenoid bone (greater wing) Supraorbital margin Superior orbital fissure Temporal bone Ethmoid bone Lacrimal bone Optic canal Inferior orbital fissure Zygomatic bone Middle nasal concha Ethmoid Perpendicular plate bone Inferior nasal concha Infraorbital foramen Maxilla Vomer Mandible Mental foramen Mental protuberance

Mandible • The lower jawbone is the largest & strongest facial bone • Composed of 2 main parts – Horizontal body – 2 upright rami

Mandible Temporomandibular joint Mandibular notch Mandibular fossa of temporal bone Coronoid process Mandibular condyle Mandibular foramen Alveolar margin Ramus of mandible Mental foramen Mandibular angle Body of mandible

Maxillary Bones (Maxillae) • Articulate with all other facial bones except the mandible • Contain maxillary sinuses largest paranasal sinuses • Forms part of the inferior orbital fissure • Are the “keystone” bones of the face

Maxillary Bones Articulates with frontal bone Frontal process Orbital surface Zygomatic process (cut) Infraorbital foramen Anterior nasal spine Alveolar margin (b) Maxilla, right lateral view

Inferior View of the Skull Hard palate Maxilla (palatine process) Palatine bone (horizontal plate) Zygomatic bone Vomer Temporal bone (zygomatic process) Mandibular fossa Styloid process Mastoid process Temporal bone (petrous part) Basilar part of the occipital bone Occipital bone External occipital crest External occipital protuberance Incisive fossa Intermaxillary suture Median palatine suture Infraorbital foramen Maxilla Sphenoid bone (greater wing) Pterygoid process Foramen ovale Foramen spinosum Foramen lacerum Carotid canal External acoustic meatus Stylomastoid foramen Jugular foramen Occipital condyle Inferior nuchal line Superior nuchal line Foramen magnum

Other Bones of the Face • Zygomatic bones – Form lateral wall of orbits (& cheekbones!) • Nasal bones – Form bridge of nose • Lacrimal bones – Located in the medial orbital walls • Palatine bones – Posterior part of the hard palate (roof of mouth) • Vomer – Forms the inferior part of the nasal septum • Inferior nasal conchae – Thin, curved bones that project medially from the lateral walls of the nasal cavity

The Cranium Bones of cranium (cranial vault) Coronal suture Squamous suture Lambdoid suture Facial bones (a) Cranial & facial divisions of the skull

The Cranium • Is the body’s most complex bony structure • Formed by cranial & facial bones • The cranium – Encloses & protects the brain – Provides attachment for head & neck muscles

Overview of Skull Geography • Facial bones form anterior aspect • Cranium is divided into cranial vault & base • Internally, prominent bony ridges divide skull into distinct fossae Anterior cranial fossa Temporal lobe of cerebrum Cerebellum Frontal lobe of cerebrum Middle cranial fossa Posterior cranial fossa (b) Superior view of the cranial fossae Cranial Posterior fossae Middle Anterior (c) Lateral view of cranial fossae showing the contained brain regions

Overview of Skull Geography • The skull contains smaller cavities – Middle & inner ear cavities in lateral aspect of cranial base – Nasal cavity lies in & posterior to the nose – Orbits house the eyeballs – Air-filled sinuses occur in several bones around nasal cavity

Overview of Skull Geography • The skull contains about 85 openings: – Foramina, canals, & fissures – Provide openings for important structures • Spinal cord • Blood vessels serving the brain • 12 pairs of cranial nerves – You do not need to learn all of these openings, only a few…. – External & internal acoustic meatus – Foramen magnum – Obturator foramen

Cranial Bones • Formed from 8 large bones – Paired bones include: • Temporal bones • Parietal bones – Unpaired bones include: • • Frontal bone Occipital bone Sphenoid bone Ethmoid bone

Parietal Bones & Sutures • Parietal bones form superior & lateral parts of skull • 4 sutures of the cranium – Coronal suture runs in the coronal plane • Located where parietal bones meet the frontal bone – Squamous suture occurs where each parietal bone meets a temporal bone inferiorly

Parietal Bones & Sutures • 4 sutures of the cranium (cont…) – Sagittal suture occurs where right & left parietal bones meet superiorly – Lambdoid suture occurs where the parietal bones meet the occipital bone posteriorly

Sutural Bones • Small bones that occur within sutures • Irregular in shape, size, & location • Not all people have sutural bones

The Skull – Posterior View Sagittal suture Parietal bone Sutural bone Lambdoid suture Occipital bone Superior nuchal line External occipital protuberance Inferior nuchal line External occipital crest Occipital condyle Occipitomastoid suture

Frontal Bone • Forms the forehead & roofs of orbits • Supraorbital margin = superior margin of orbits (=brow) • Glabella = smooth part of frontal bone between superciliary arches – Frontal sinuses within frontal bone • Contributes to anterior cranial fossa

Occipital Bone • Forms the posterior portion of the cranium & cranial base • Articulates with the temporal bones & parietal bones • Forms the posterior cranial fossa • Foramen magnum located at its base

Occipital Bone • Features & structures: – Occipital condyles – Hypoglossal foramen – External occipital protuberance – Superior nuchal lines – Inferior nuchal lines

Inferior Aspect of the Skull Hard palate Maxilla (palatine process) Palatine bone (horizontal plate) Zygomatic bone Vomer Temporal bone (zygomatic process) Mandibular fossa Styloid process Mastoid process Temporal bone (petrous part) Basilar part of the occipital bone Occipital bone External occipital crest External occipital protuberance Incisive fossa Intermaxillary suture Median palatine suture Infraorbital foramen Maxilla Sphenoid bone (greater wing) Pterygoid process Foramen ovale Foramen spinosum Foramen lacerum Carotid canal Ext. acoustic meatus Stylomastoid foramen Jugular foramen Occipital condyle Inferior nuchal line Superior nuchal line Foramen magnum

Temporal Bones • Lie inferior to parietal bones • Form the inferolateral portion of the skull • Term “temporal” comes from Latin word for time • Specific regions of temporal bone: – Squamous, tympanic, petrous, & mastoid regions

Lateral Aspect of the Skull Frontal bone Coronal suture Sphenoid bone (greater wing) Parietal bone Ethmoid bone Lacrimal bone Squamous suture Nasal bone Temporal bone Lacrimal fossa Zygomatic bone Zygomatic process Lambdoid suture Coronoid process Maxilla Occipital bone External occipital protuberance Alveolar margins Occipitomastoid suture Mandible Mental foramen External acoustic meatus Mastoid process Mandibular condyle Styloid process Mandibular notch Mandibular ramus Mandibular angle

The Temporal Bone External acoustic meatus Squamous region Mastoid region Zygomatic process Mastoid process Mandibular fossa Styloid process Tympanic region

The Temporal Bone • The mastoid process – Site for neck muscle attachment – Contains air sinuses • Petrous region – Projects medially, contributes to cranial base – Houses cavities of middle & internal ear • Contributes to the middle & posterior cranial fossae

The Temporal Bone • Foramina of the temporal bone – Jugular foramen – Carotid canal – Foramen lacerum – Extermal & Internal accoustic meatus

Inferior Aspect of the Skull Hard palate Zygomatic bone Zygomatic process of temporal bone Foramen ovale Foramen spinosum Mandibular fossa Foramen lacerum Carotid canal Mastoid process Styloid process Jugular foramen Occipital condyle Foramen magnum Superior nuchal line

The Sphenoid Bone • • • Spans the width of the cranial floor Resembles a butterfly or bat! Consists of a body & 3 pairs of processes Contains 5 important openings Is the “keystone” of the cranium

The Sphenoid Bone Optic canal Greater wing Sella turcica Lesser wing Foramen rotundum Foramen ovale Foramen spinosum Body of sphenoid (a) Superior view Figure 7. 10 a

The Sphenoid Bone Body of sphenoid Lesser wing Superior orbital fissure Greater wing Pterygoid process (b) Posterior view Figure 7. 10 b

The Ethmoid Bone • Lies between nasal & sphenoid bones • Forms most of the medial bony region between the nasal cavity & orbits

The Ethmoid Bone • Cribriform plate superior surface of the ethmoid bone – Contains olfactory foramina (= holes for olfactory neurons) • Crista galli attachment site for falx cerebri (=strong sheet of dura matter between right & left cerebral hemispheres) • Perpendicular plate forms superior part of nasal septum • Lateral masses contain air cells (nasal sinuses) • Superior & middle nasal conchae – Extend medially from lateral masses

The Ethmoid Bone Crista galli Olfactory foramina Orbital plate Cribriform plate Left lateral mass Ethmoidal air cells Perpendicular plate Middle nasal concha

Special Parts of the Skull • • Orbits Nasal cavity Paranasal sinuses Hyoid bone

Nasal Cavity Superior, middle, & inferior meatus Frontal sinus Superior nasal concha Ethmoid Middle bone nasal concha Inferior nasal concha Nasal bone Anterior nasal spine Sphenoid bone Maxillary bone (palatine process) Sphenoid sinus Pterygoid process Palatine bone (perpendicular plate) Palatine bone (horizontal plate) (a) Bones forming the left lateral wall of the nasal cavity (nasal septum removed)

Nasal Septum Ethmoid bone Crista galli Cribriform plate Frontal sinus Sella turcica Nasal bone Sphenoid sinus Perpendicular plate of ethmoid bone Septal cartilage Vomer Palatine bone Hard palate Palatine process of maxilla Alveolar margin of maxilla (b) Nasal cavity with septum in place showing the contributions of the ethmoid bone, the vomer, & septal cartilage

Paranasal Sinuses • Air-filled sinuses are located within – Frontal bone – Ethmoid bone – Sphenoid bone – Maxillary bones • Lined with mucous membrane • Lighten the skull

Paranasal Sinuses Frontal sinus Ethmoidal air cells (sinus) Sphenoid sinus Maxillary sinus (a) Anterior aspect Frontal sinus Ethmoidal air cells Sphenoid sinus Maxillary sinus (b) Medial aspect

Orbits Supraorbital notch Roof of orbit Lesser wing of sphenoid bone Orbital plate of frontal bone Lateral wall of orbit Zygomatic process of frontal bone Greater wing of sphenoid bone Orbital surface of zygomatic bone Superior orbital fissure Infraorbital groove Zygomatic bone Optic canal Medial wall Sphenoid body Orbital plate of ethmoid bone Frontal process of maxilla Lacrimal bone Nasal bone Floor of orbit Orbital process of palatine bone Orbital surface of maxillary bone Infraorbital foramen (b) Contribution of each of the 7 bones forming the right orbit Zygomatic bone

The Hyoid Bone • Lies inferior to the mandible • The only bone with no direct articulation with any other bone • Acts as a movable base for the tongue Greater horn Lesser horn Body

Questions…? What’s Next? Lab Today: Bones Wed Lecture: Appendicular Skeleton Wed Lab: Finish Bones; Selected Joints