Anatomy Notes- Outline, Week 3
Anatomy Notes- Outline, Week 3 3244
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This 15 page Class Notes was uploaded by Alexandra Notetaker on Friday September 9, 2016. The Class Notes belongs to 3244 at University of Colorado Denver taught by Dr. Kent Nofsinger in Fall 2016. Since its upload, it has received 9 views. For similar materials see Human Anatomy in Biology at University of Colorado Denver.
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Date Created: 09/09/16
III. Gross Anatomy of the “Typical” Long Bone A typical long bone is composed of several different parts that are the same regardless of the bone. These include: A. Diaphysis 1. The shaft of a long bone, the cylinder of compact bone surrounding a central cavity. 2. The shaft normally applies forces from one epiphysis to the other, and is very strong when stressed along that axis. 3. However when stressed tangentially (from the sides), it is more likely to fracture. B. Epiphysis 1. The ends of a long bone, consists of spongy bone surrounded by compact bone a) Compact bone (dense bone) – is hard and dense, and is the protective exterior portion of all bones. b) Spongy bone (cancellous bone) – is deep to the compact bone, and quite porous, forms an open network of struts and branching plates (trabeculae) which are oriented along stress lines, but with extensive cross bracing. C. Metaphysis or Epiphyseal End plate 1. A relatively narrow zone where the diaphysis joins the epiphysis D. Medullary cavity containing red or yellow marrow 1. Central cavity found in long bones, usually surrounded by spongy bone 2. Yellow marrow – contains large amounts of fat 3. Red marrow where hemopoiesis (process of blood cell formation) occurs – portions of the vertebrae, sternum, ribs, skull, scapulae, pelvis, and proximal limb bones E. Endosteum 1. Lining of the medullary cavity by a thin layer of connective tissue F. Periosteum 1. The outer surface covering of a bone except over articular cartilage; it consists of a layer of dense irregular CT with an inner cellular layer. G. Articular cartilage 1. Thin layer of hyaline cartilage that caps long bone epiphyses, and facilitates joint movement. II. Histology of Bone A. Compact Bone: the smooth outer surface of all bone Compact bone is largely composed of a histological unit called either the osteon or the Haversian System. You will see both in the literature, and will hear both terms used interchangeably. 1. The Osteon: concentric lamellae a) Concentric circular lamellae around the central canal. b) Collagen fibers spiral around the lamella; variations in the direction of spiraling between adjacent lamellae strengthen the osteon. c) Central Canal or Haversian Canal (1) The center of the osteon which contains minute blood vessels and a nerve (2) The canal runs parallel to the length of the long bone, and the normal stresses of force d) Perforating Canal or Volkmann’s Canal (1) Extend roughly perpendicular to the surface of the bone and the osteons (2) Connect the osteon vessels and nerves to larger trunks e) Lacunae (1) Small pockets or cavities occupied by osteocytes, regularly arranged between the lamellae f)Canaliculi (1) Little channels which radiate through the matrix of the lacuna (2) Contain osteocytes cytoplasmic processes, and allow diffusion of nutrients and waste through ground substance, or intercellular gap junctions g)Osteoid: the organic part of the bone matrix; made of calcium phosphate and various types of compounds that make up matrix 2. Interstitial lamellae – the 2nd type of lamellae a) Fill in the spaces between the osteon in compact bone b)Also have lacunae and canaliculi c) May have been produced during the growth of the bone, or represent remnants of osteons 3. Circumferential lamellae – the 3rd type of lamellae a) Each of these extends around the entire circumference of the diaphysis, along the internal and external surfaces B. Spongy Bone 1. aka trabecular bone – composed of trabeculae – little “struts” 2. The trabeculae line up along lines of stress 3. The space between the trabeculae is filled with yellow or red marrow C. Medullary cavity 1. The interior of all bone consists of spongy bone, however in the very center of long bone diaphyses, there is no bone tissue at all, and it is filled with yellow marrow mostly III. Types of Cells found in bone A. Osteogenic or osteoprogenitor cells: found in bone along the periosteum and endosteum; in response to a fracture or trauma, they give rise to osteoblasts and osteoclasts; stem cells for bone only B. Osteoblasts: immature bone cells; cuboidal shaped cells that form bone. They secrete the organic materials of the bone matrix that become mineralized by an unknown mechanism. Found in periosteum and endosteum C. Osteocytes: mature bone cells that regulate the protein and mineral content of the surrounding matrix. Can release or deposit calcium to the surrounding matrix. They are located inside lacunae D. Osteoclasts: giant cells with 50 or more nuclei. They secrete acid, which dissolve the bony matrix in a process called osteolysis. 1. Osteoclasts are always removing matrix and releasing minerals, and osteoblasts are always producing matrix that quickly binds minerals IV. Ossification of Bone There are two major pathways by which osseous tissue is formed during embryonic development. These include what are known as intramembranous ossification and endochondrial ossification. A. Intramembranous (dermal ossification): In the fetus, bone develops from mesenchyme or fibrous connective tissue The roof bones of the skull, the mandible, clavicle, and patella form this way. 1Step One - Mesenchymal cells differentiate into osteoblasts, which cluster together, and secrete the organic components of the matrix. The collagen and osteoid then become mineralized. These sites are called ossification centers. 1. Step Two - The developing bone grows outward from the ossification centers in struts called spicules. Osteoblasts become entrapped in the expanding bone, but mesenchymal cells continue to differentiate, adding new osteoblasts. Blood vessels branch within the region. 2. Step Three: The bone assumes the structure of spongy bone. Subsequent remodeling around the trapped blood vessels can produce compact bone. B. Endochondral ossification Occurs in limb bone development of the embryo/fetus. A hyaline cartilage model is formed. 1. Step One: As the cartilage enlarges, chondrocytes near the center of the shaft enlarge, and the matrix calcifies. The chondrocytes die. 2. Step Two: The perichondrium surrounding the cartilage model is going to become periosteum, and produce cells that differentiate into osteoblasts. The perichondrium is now periosteum, and the inner layer (osteogenic layer) produces a thin layer of bone around the shaft of the cartilage (bone collar). 3. Step Three: Blood to the periosteum increases, and osteoblasts migrate into the cartilage and invade the spaces left by the chondrocytes. The calcified cartilaginous matrix breaks down, and the osteoblasts replace it with spongy bone. Bone development proceeds from the primary ossification center in the shaft towards both ends of the cartilage model. 4. Step Four: As the diameter of the diaphysis enlarges, the osteoclasts erode the center, and create a marrow cavity. Further growth involves increase in length and increase in diameter. 5. Step Five: At the ends of the bone, cartilage is being replaced by bone at the metaphysis. On the shaft side, osteoblasts are continually invading the cartilage and replacing it with bone. On the epiphyseal side, new cartilage is produced at the same rate. 6. Step Six: Around birth, some of the epiphyseal cartilages calcify, creating secondary ossification centers. The cartilage at the metaphysis is called the epiphyseal plate. 7. The epiphyseal plate contains 5 zones: a) Reserve zone - small chondrocytes irregularly dispersed b) Proliferation zone - larger regularly arranged chondrocytes c) Hypertrophic zone - large chondrocytes arranged in columns. Where the growth of long bones actually occurs. Like cartilage, this would be called interstitial growth as the bone lengthens d) Resorption zone - where the mineral content change occurs e) Ossification zone - a region of transformation from cartilage to bone Vocabulary Axial Diaphysis Interstitial lamellae Appendicular Epiphysis Central canal (Haversian Hematopoiesis Metaphysis canal) (hemopoiesis) Medullary cavity Perforating canal Metacarpal Endosteum (Volkmann’s canal Metatarsal Periosteum Lacunae Phalanges Articular Canalicula (pl: canaliculi) Sesamoid Concentric lamellae Osteon Osteogenic cells Osteoclasts Endochondral Osteoblasts Intramembranous ossification Osteocytes ossification Gross Anatomy of Bone Much of the gross anatomy of the bone will be covered in the lab. Unfortunately, time constraints limit the amount of time that we can give to this topic. The lecture will concern itself with the general features of bone. I The Skull C. General Features 1. Cranial bones (8): enclose the brain and sensory organs 2. Facial bones (14): frame the face and support the teeth 3. Cavities: a) Cranial – largest with capacity of 1300-1350 cc. Formed by cranial and facial bones b) Nasal – divided into 2 nasal fossae by a nasal septum c) Paranasal sinuses (4 sets): frontal, ethmoidal, sphenoidal, maxillary sinuses d) Middle and inner ear cavities e) Orbital f) Oral or buccal cavity – only partially lined by bone 4. Fontanels: fetal and infant cranial bones not fused, but covered with connective tissue a) Allow for molding and growing b) Ossification complete by 20-24 months c) Anterior: most prominent, diamond shaped d) Posterior: smaller, diamond shaped e) Anterolateral: small and irregular, paired f)Posterolateral: small and irregular, paired 5. Sutures – a fibrous joint found between bones of the skull - covered in lab a) Sagittal b)Coronal c) Lambdoid d) Squamous 6. Foramina: an opening in an anatomical structure; usually a bone -covered in lab a) Refer to Table 7.1 for list of Major Foramina 7. Associated bones - not part of skull but associated with it: a) Hyoid – unique doesn’t directly attach to any other bone b) Auditory Ossicles: malleus, incus, and stapes V. Cranial bones A. Frontal – fuse by age 6 1. Contains frontal sinuses 2. Supraorbital margin 3. Supraorbital foramen: supraorbital nerves and a B. Parietal C. Temporal 1. Squamous – flat plate at sides of skull a) Includes zygomatic process, and mandibular fossa 2. Tympanic part – a) External acoustic meatus (passageway or canal) b) Styloid process (supports hyoid and some tongue muscles) 3. Mastoid – a) Stylomastoid foramen allows passage of the facial nerve 4. Petrous part = rocky – the floor of cranium a) Carotid canal – anterior b) Jugular foramen – more posterior D. Occipital bone 1. Foramen magnum – houses spinal cord 2. Occipital condyles on each side which articulate with C1 (the atlas) 3. Hypoglossal canal – anterolateral edge of condyles 4. External occipital protuberance 5. Superior nuchal line: a bony ridge extending laterally E. Sphenoid bone 1. Lesser wing a) Optic canals – through lesser wing 2. Greater wing a) Superior orbital fissures between lesser and greater wings 3. Body a) Foramen rotundum – opening just posterior to superior orbital fissure; maxillary n passes through b) Foramen lacerum – between sphenoid and petrous part of the temporal bone; no major nerves or vessels c) Sella turcica – houses pituitary gland 4. Lateral pterygoid plate a) Foramen ovale -- allows passage of the mandibular nerve b) Foramen spinosum – small opening at posterior angle of sphenoid through which middle meningeal vessels pass F. Ethmoid bone 1. Perpendicular plate - inferior projection that divides forms superior nasal septum 2. Cribriform plate – numerous foramina for passage of olfactory nerves 3. Crista galli – attachment for meninges 4. Superior and middle concha – turbinate (especially of a shell) shaped like a spinning top or inverted cone Bone Foramina* Structures Transmitted Frontal bone Supraorbital foramen Supraorbital nerve, artery, and vein; ophthalmic nerve Parietal bone Parietal foramen Emissary vein of superior sagittal sinus Carotid canal Internal carotid artery External acoustic meatus Sound waves to eardrum Vestibulocochlear and facial nerves; internal Temporal bone Internal acoustic meatus auditory vessels Stylomastoid foramen Facial nerve Mastoid foramen Meningeal artery; vein from sigmoid sinus Internal jugular vein; glossopharyngeal, Temporal-occipital region Jugular foramen vagus, and accessory nerves Temporal-occipital- Foramen lacerum No major nerves or vessels; closed by sphenoid region cartilage Spinal cord; accessory nerve; vertebral Foramen magnum arteries Occipital bone Hypoglossal canal Hypoglossal nerve to muscles of tongue Condylar canal Vein from transverse sinus Foramen ovale Mandibular division of trigeminal nerve; accessory meningeal artery Foramen rotundum Maxillary division of trigeminal nerve Middle meningeal artery; spinosal nerve; part Foramen spinosum of trigeminal nerve Sphenoid bone Optic foramen Optic nerve; ophthalmic artery Oculomotor, trochlear, and abducens nerves; Superior orbital fissure ophthalmic division of trigeminal nerve; ophthalmic veins Ethmoid bone Olfactory foramina Olfactory nerves Infraorbital foramen Infraorbital nerve and vessels Maxilla Incisive foramen Nasopalatine nerves Lacrimal bone Lacrimal foramen Tear duct leading to nasal cavity Palatine bone Greater palatine Palatine nerves foramen in each bone Zygomaticofacial Zygomaticofacial nerve – sensory nerve to Zygomatic bone cheek from mandibular branch of trigeminal foramen nerve Mental foramen Mental nerve and vessels Mandible Inferior alveolar nerves and vessels to the Mandibular foramen lower teeth *When two or more bones are listed together (for example, temporal-occipital), it indicates that the foramen passes between them. Memory Trick: Remember the pituitary cowboy that sits in the sella turcica, his name is ROS. He is named ROS for the three foramina on either side; from medial to lateral: Rotundum , Ovale, Spinosum. His Legs go through Lacerum and his arms go through the optic canal. Optic Foramen or canal Foramen Rotundum Foramen Ovale Foramen Spinosum Foramen Lacerum Sella Turcica VI. Facial bones Except for vomer and mandible, all facial bones are paired A. Maxillary bones: jawbone 1. Anchors teeth: incisors, canines, premolars (bicuspids) and molars in dental alveoli 2. Palatine process – greater portion of hard palate 3. Incisive foramen 4. Infraorbital foramen – infraorbital nerve and artery 5. Maxillary sinus – the largest of the paranasal sinuses 6. Alveolar process—houses the teeth B. Palatine bones 1. Form posterior 1/3 of hard palate, nasal cavity and eye orbit 2. Horizontal plate—articulates anteriorly w/ the palatine process of the maxilla 3. Palatine foramina—greater and lesser foramina 4. Perpendicular plate—forms part of nasal cavity and orbit 5. Orbital process C. Zygomatic bones: cheekbones 1. Unites with temporal bone to form zygomatic arch which consists of zygomatic process of temporal bone and temporal process of zygomatic bone 2. Frontal process 3. Maxillary process 4. Temporal process D. Lacrimal bone: lacrima = a tear 1. Smallest of facial bones 2. Groove houses nasolacrimal canal E. Nasal bones 1. Paired 2. Form bridge of the nose F. Inferior nasal conchae 1. Curved bones that project from lateral walls of nasal cavity G. Vomer 1. Forms lower part of nasal septum 2. Supports nasal cartilage with the perpendicular plate H. Mandible: lower jaw 1. Largest and strongest facial bone 2. Body – front and lateral sides 3. Rami – extend vertically from body 4. Condylar process – articulates with temporal bone 5. Coronoid process – attachment of temporalis muscle 6. Mandibular notch 7. Mental foramen – mental nerve and vessels 8. Mandibular foramen – inferior alveolar nerve and vessels I. Hyoid 1. Suspended from styloid process by stylohyoid muscles and ligaments 2. Supports tongue 3. Frequently fractured in strangulation 4. Lesser cornu and Greater cornu J. Auditory Ossicles: tiny ear bones 1. Malleus 2. Incus 3. Stapes VII. Vertebral Column: will speak only in general terms; you are responsible for specifics from text and in lab A. Functions 1. Support head and upper extremities 2. Provide attachment for muscles, ribs, organs 3. Protect the spinal cord 4. Helps maintain upright body position 5. Provides a passageway for spinal nerves that connect to the spinal cord B. Usually 33 vertebrae 1. 7 cervical 2. 12 thoracic 3. 5 lumbar 4. 5 (3-5) sacral - fused 5. 4 (3-5) coccyx – fused 6. Typically 26 movable parts of vertebral column C. General structure 1. Separated from each other by fibrocartilaginous intervertebral discs 2. Intervertebral foramina – openings between vertebrae through which spinal nerves pass 3. Body – anterior cylindrical portion 4. Vertebral foramen – houses part of spinal cord Vertebral pedicles – lateral wall of foramen Vertebral lamina – arched; connected to } The pedicles and lamina form the vertebral pedicles arch 5. 7 processes – a) Spinous process - bifurcated posterior process: for muscle attachment b) 2 transverse processes: for muscle attachment c) 2 superior articular processes: limit twisting d) 2 inferior articular processes: limit twisting D. Sacrum 1. Superior articular process 2. Promontory 3. Anterior sacral foramina 4. Posterior sacral foramina 5. Ala—upper surface, wing-like structures 6. Transverse ridges or lines 7. Sacral canal 8. Sacral cornu 9. Median sacral crest 10.Sacral hiatus 11.Auricular surface—the “ears” of the sacrum E. Coccyx: attaches inferiorly to sacrum 1. Attachment site for several ligaments and some muscles F.Spinal curves 1. Cervical 2. Thoracic 3. Lumbar 4. Sacral Pathology a) Kyphosis -- exaggeration of normal thoracic curve b) Lordosis – exaggeration of the lumbar curve resulting in prominent abdomen and buttocks c) Scoliosis – abnormal lateral curve, most often seen in adolescent females VIII. Rib Cage A.Sternum 1. 3 bones: manubrium, body, xiphoid process 2. Manubrium: the widest and most superior portion of the sternum; the “handle” of the bony sword a) Jugular notch/suprasternal notch: shallow superior indentation between the clavicular notches b) Clavicular notch: articulate the sternum w/ the L and R clavicles st nd c) Articulates with the costal cartilage of the 1 and 2 ribs 3. Body: the longest part of the sternum; the “blade” of the sword nd th a) Athacths to theth through 10 ribs b) 8 , 9 , and 10 costal cartilages fuse to form the costal margin c) Costal angle where the costal cartilages come together with the xiphoid process 4. Xiphoid process: the tip of the “sword blade”; cartilaginous a) Attachment for muscles b) Usually not ossified before age 25 B.Ribs 1. 12 pair st th 2. 7 pair (1 -7 ) anchored to sternum by individual costal cartilages: TRUE ribs 3. Remaining 5 pair (8 th– 12 ): FALSE ribs; their costal cartilages don't attach threctly tththe sternum 4. 11 and 12 don’t attach to sternum at all: FLOATING ribs; no connection to the sternum 5. Head of the rib articulates at a costal facet on the thoracic vertebral body and the tubercle of rib articulates at the transverse costal facet on the transverse process of the thoracic vertebral body 6. Neck constricted area between head and tubercle 7. Body – curved main part of rib 8. Costal groove – depressed inner canal that protects costal veins and nerves 9. Costochondral joint 10. Intercostal spaces IX. Diseases of bone A. Developmental 1. Spina bifida: congenital defect where the vertebral laminae fail to fuse 2. Cleft palate/cleft lip: vary in severity B. Nutritional/hormonal 1. Rickets: Vitamin D deficiency in children 2. Osteomalacia: demineralization due to Vitamin D deficiency in adults 3. Gigantism: hypersecretion of growth hormone prior to ossification of growth plates 4. Acromegaly: hypersecretion of growth hormone after ossification of growth plates, resulting in hypertrophy of the bones of the face, hands, and feet 5. Dwarfism: growth hormone deficiency C. Neoplasms (neo=new and plasm=substance, tissue; hence a tumor) 1. Osteoma – benign tumor of bone, often the skull 2. Osteoid osteomas – painful benign tumors of long bones 3. Osteogenic sarcoma – malignant (cancerous) tumor D. Aging 1. Osteoporosis— weakening of bones as a result of calcium loss; Causes— aging, inactivity, poor diet, hormonal imbalance Appendicular Skeleton I Pectoral Girdle and Upper Extremity E. General 1. The pectoral girdle is composed of the scapulae and the clavicles. 2. The brachium: upper arm 3. The antebrachium: forearm 4. Wrist 5. Hand 6. The pectoral girdle is only attached to the axial skeleton at the sternoclavicular joint a) Allows wide range of movement b) Structurally more delicate The brachium extends from the shoulder to the elbow; in anatomy the arm strictly refers to the brachium F. The Clavicle: the “collar bone” 1. Slender S-shaped bone just deep to the skin 2. Sternal end: towards the sternoclavicular joint 3. Acromial end: towards the acromioclavicular joint: the junction with the scapula 4. Costal tuberosity: towards the sternal end - attachment site for shoulder ligaments 5. Conoid tubercle: (cone-shaped); towards the acromial end – attachment site for shoulder ligaments 6. Most frequently fractured bone G. The Scapula: the “shoulder blade” 1. Overlies ribs 2-7 2. The “spine” – strengthens the scapula, diagonal bony ridge on posterior surface 3. Suprascapular notch 4. Supraspinous fossa—posterior depression 5. Infraspinous fossa—posterior depression 6. Subscapular fossa—anterior surface 7. Glenoid cavity/fossa: resembles a socket; below acromion, where the humerus will fit 8. Infraglenoid and Supraglenoid tubercle 9. Coracoid process (like a “crow’s beak”) a) Anterior and superior to glenoid cavity b) Serves as the attachment for the biceps brachii 10.Acromion process (akron = tip, omos = shoulder) a) Larger process, posterior b) Attachment site for part of the trapezius muscle c) Articulates with the acromial end of the clavicle – the acromioclavicular joint 11. Borders: superior, medial (closest to vertebrae), and lateral (closest to axilla) H. Humerus: longest and largest upper limb bone; 1 bone of the brachium 1. Proximal head—articulates with the glenoid cavity of scapula 2. Greater tubercle 3. Lesser tubercle 4. Intertubercular sulcus: groove between the greater and lesser tubercles; biceps brachii muscle tendon passes through 5. Anatomical neck—groove that marks the location of the former epiphyseal plate 6. Surgical neck – frequent site of fractures; narrowing of the bone immediately distal to the tubercles at the transition from the head to the shaft 7. Deltoid tuberosity – where deltoid inserts 8. Radial groove—can be seen on posterior view; located adjacent deltoid tuberosity 9. Medial and lateral epicondyles—located distally 10. Capitulum (caput = head): articulates with head of radius; located laterally 11. Radial fossa—depression located anteriorly and superior to capitulum 12. Coronoid fossa—depression located anteriorly and superior to trochlea 13. Trochlea (pulley-shaped, posterior view): articulates with the trochlear notch of the ulna; located medially 14. Olecranon fossa – depression located posteriorly and superior to trochlea; allow movement of ulna I. Radius: lateral side of forearm 1. Head—proximal end that articulates with the capitulum of the humerus 2. Neck—separates the radial head from the radial tuberosity—attachment site for the biceps brachii muscle 3. Shaft—curves slightly and leads to a wide distal end where there’s a styloid process—bony projection on lateral side of wrist 4. Ulnar notch—distal, medial surface that articulates with the distal end of the ulna J. Ulna: medial side of forearm; “Elbow” 1. Head—distal end that has a posteromedial styloid process that is located on the “little finger” side of the wrist 2. Tuberosity of the ulna—proximal end 3. Trochlear notch—interlocks with the trochlea of the humerus; C-shaped 4. Olecranon—articulates with the olecranon fossa of the humerus and forms the posterior “bump” of the elbow 5. Coronoid process—inferior lip of the trochlear notch 6. Radial notch—accommodates the head of the radial and helps form the proximal radioulnar joint; lateral to the coronoid process Both the radius and the ulna exhibit interosseous borders which face each other; the ulna’s interosseous border projects laterally and the radius’s projects medially These borders are connected by an interosseous membrane composed of dense irregular connective tissue that helps keep the radius and ulna a fixed distance apart form other another and provides a pivot of rotation for the forearm K. Pathology Lateral epicondylitis: tennis elbow due to six extensor muscles of hand and wrist that originate here When falling, we naturally extend our hands to break the fall; frequent fractures of the radial head, neck or distal end (Colle’s) fracture can occur. It is less traumatic to pull appendages in, and let a larger body surface his the ground. Radial head dislocation or "pulled elbow": in children less than five, usually associated with forceful pulling of hand. Symptoms: immediate pain, and flexion of the elbow, with the child resisting extension. The treatment is firm supination of the hand with the elbow held at 90 flexion. The hand consists of 27 bones grouped into the carpals, metacarpals, and phalanges L. Carpus: the true wrist – 8 carpal bones of wrist 1. Proximal row from lateral to medial (anatomical position) a) Scaphoid: (skaphe = boat); accounts for 70% of wrist fractures b) Lunate: (luna = moon) c) Triquetrum: (triquetrus = three cornered) d) Pisiform: (pisum = pea) 2. Distal row from lateral to medial a) Trapezium b) Trapezoid c) Capitate d) Hamate Mental trick: Some Lovers Try Positions That They Can’t Handle Scaphoid, lunate, triquetrum, pisiform, trapezium, trapezoid, capitate, hamate M. Metacarpal bones: support the palm of the hand 1. One for each digit; I-V (I at base of thumb and V at base of little finger) 2. Proximal base 3. Body 4. Distal head N. Phalanges (sing: phalanx) 1. 14 bones of the digits on each hand (3 on each except thumb which lacks a middle phalanx) 2. Proximal (articulates with the head of a metacarpal), middle and distal phalanx (tip of finger) 3. Digits numbered I-V 4. The thumb has only 2 phalanges; thumb is called the pollex
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