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OSTEOLOGY
23. September.2011 Friday
Osteology (Gk, osteon, bone, logos, science) is the branch of medicine concerned with the
development and diseases of bone tissue. The human skeleton is composed of 206 bones in adults.
The skeletal system may be divided into two functional parts:
 The axial skeleton consists of the bones of the head (cranium or skull), neck (hyoid bone and cervical
vertebrae), and trunk (ribs, sternum, vertebrae, and sacrum).
 The appendicular skeleton consists of the bones of the limbs, including those forming the pectoral
(shoulder) and pelvic girdles.
Bone is one of the hardest structures of the animal body, because of the calcification of its
extracellular matrix. Living bones have some elasticity (results from the organic matter) and great rigidity
(results from their lamellous structures and tubes of inorganic calcium phosphate). Its color, in a fresh state,
is pinkish-white externally, and deep red within.
Cartilage and Bones
The skeleton is composed of cartilages and bones. Cartilage is a resilient, semirigid form of
connective tissue that forms parts of the skeleton where more flexibility is required—for example, where the
costal cartilages attach the ribs to the sternum. Also, the articulating surfaces (bearing surfaces) of bones
participating in a synovial joint are capped with articular cartilage that provides smooth, low-friction, gliding
surfaces for free movement. Blood vessels do not enter cartilage (i.e., it is avascular); consequently, its cells
obtain oxygen and nutrients by diffusion. The proportion of bone and cartilage in the skeleton changes as the
body grows; the younger a person is, the more cartilage he or she has. The bones of a newborn are soft and
flexible because they are mostly composed of cartilage.
Bone has a protective function; the skull and vertebral column, for example, protect the brain and
spinal cord from injury; the sternum and ribs protect the thoracic and upper abdominal viscera. It serves as a
lever, as seen in the long bones of the limbs, and as an important storage area for calcium salts. It houses and
protects within its cavities the delicate blood-forming bone marrow.
Bones are classified according to their shape (gross anatomy):
1) Long bones are tubular (e.g., the humerus in the arm).
2) Short bones are cuboidal and are found only in the tarsus (ankle) and carpus (wrist).
3) Flat bones usually serve protective functions (e.g., the flat bones of the cranium protect the brain).
4) Irregular bones have various shapes other than long, short, or flat (e.g., bones of the face).
5) Sesamoid bones (e.g., the patella or knee cap) develop in certain tendons and are found where tendons
cross the ends of long bones in the limbs; they protect the tendons from excessive wear and often change the
angle of the tendons as they pass to their attachments.
There are two types of bones according to histological features: compact bone and spongy (trabecular) bone.
They are distinguished by the relative amount of solid matter and by the number and size of the spaces they
contain All bones have a superficial thin layer of compact bone around a central mass of spongy bone,
except where the latter is replaced by a medullary (marrow) cavity. Spongy bone is found at the expanded
heads of long bones and fills most irregular bones. Compact bone forms the outer shell of all bones and also
the shafts in long bones.
Bone Markings and Formations
Bone markings appear wherever tendons, ligaments, and fascias are attached or where arteries lie
adjacent to or enter bones. Other formations occur in relation to the passage of a tendon (often to direct the
tendon or improve its leverage) or to control the type of movement occurring at a joint. Surfaces of the bones
are not smooth. Bones display elevations, depressions and holes. The surface features on the bones are given
names to distinguish and define them.
Vasculature and Innervation of Bones
Bones are richly supplied with blood vessels. Veins accompany arteries. Nerves accompany blood
vessels supplying bones.
SKULL BONES
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The skull is supported on the summit of the vertebral column, and is of an oval shape, wider behind
than in front. It is composed of a series of flattened or irregular bones which, with one exception (the
mandible), are immovably jointed together. It is divisible into two parts: (1) the cranium, which lodges and
protects the brain, consists of eight bones, and (2) the skeleton of the face, of fourteen, as follows:
Occipital.
Two Parietals.
Frontal.
Cranium, 8 bones
Two Temporals.
Sphenoidal.
Ethmoidal.
Two Nasals.
Two Maxillæ.
Two Lacrimals.
Two Zygomatics.
Face, 14 bones
Two Palatines.
Two Inferior Nasal Conchæ.
Vomer.
Mandible.
Ossa Cranii
The Occipital bone: situated at the back and lower part of the cranium, is trapezoid in shape and
curved on itself. It is pierced by a large oval aperture, the foramen magnum, through which the cranial cavity
communicates with the vertebral canal. The curved, expanded plate behind the foramen magnum is named
the squama; the thick, somewhat quadrilateral piece in front of the foramen is called the basilar part, whilst
on either side of the foramen is the lateral portion.
The Parietal Bones: form, by their union, the sides and roof of the cranium. Each bone is irregularly
quadrilateral in form. The external surface is convex, smooth, and marked near the center by an eminence,
the parietal eminence (tuber parietale). Crossing the middle of the bone in an arched direction are two curved
lines, the superior and inferior temporal lines.
The Frontal Bone: resembles a cockle-shell in form, and consists of two portions—a vertical
portion, the squama, corresponding with the region of the forehead; and an orbital or horizontal portion,
which enters into the formation of the roofs of the orbital and nasal cavities.
Some prominent features of the frontal bone:
Zygomatic process: is the part of the zygomatic process consisting of the frontal bone.
Foramen cecum: The frontal crest of the frontal bone ends below in a small notch which is converted into a
foramen, the foramen cecum (or foramen caecum), by articulation with the ethmoid.
The Temporal Bones: are situated at the sides and base of the skull. Each consists of five parts, viz.,
the squama, the petrous, mastoid, and tympanic parts, and the styloid process.
Some prominent features of the temporal bone:
Zygomatic process: projects from the lower part of the squama as a long, arched process.
The Sphenoid Bone: is situated at the base of the skull in front of the temporals and basilar part of the
occipital. It somewhat resembles a bat with its wings extended, and is divided into a median portion or body,
two great and two small wings extending outward from the sides of the body, and two pterygoid processes
which project from it below.
Some prominent features of the sphenoid bone:
Tuberculum sellæ: behind the chiasmatic groove is an elevation, the tuberculum sellae; and still more
posteriorly, a deep depression, the sella turcica, the deepest part of which lodges the hypophysis cerebri and
is known as the fossa hypophyseos (or fossa hypophysialis).
Skull, 22 bones
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Clivus: (Latin for "slope") is a part of the cranium, a shallow depression behind the dorsum sellæ that slopes
obliquely backward.
The Ethmoid bone: is exceedingly light and spongy, and cubical in shape; it is situated at the
anterior part of the base of the cranium, between the two orbits, at the roof of the nose, and contributes to
each of these cavities.
Cranial Fossas
The inferior and anterior parts of the frontal lobes of the brain occupy the anterior cranial fossa, the
shallowest of the three cranial fossae. The fossa is formed by the frontal bone anteriorly, the ethmoid bone in
the middle, and the body and lesser wings of the sphenoid posteriorly. The butterfly-shaped middle cranial
fossa has a central part composed of the sella turcica on the body of the sphenoid and large, depressed lateral
parts on each side. The posterior cranial fossa, the largest and deepest of the three cranial fossae. The
posterior cranial fossa is formed mostly by the occipital bone.
The Facial Bones
1. The Nasal Bones: are two small oblong bones, varying in size and form in different individuals;
they are placed side by side at the middle and upper part of the face, and form, by their junction, “the bridge”
of the nose. Each has two surfaces and four borders.
2. The Maxillæ (Upper Jaw): are the largest bones of the face, excepting the mandible, and form, by
their union, the whole of the upper jaw. Each assists in forming the boundaries of three cavities, viz., the
roof of the mouth, the floor and lateral wall of the nose and the floor of the orbit; it also enters into the
formation of two fossæ, the infratemporal and pterygopalatine, and two fissures, the inferior orbital and
pterygomaxillary. Each bone consists of a body and four processes—zygomatic, frontal, alveolar, and
palatine.
3. The Lacrimal Bone: the smallest and most fragile bone of the face, is situated at the front part of
the medial wall of the orbit.
4. The Zygomatic Bone (Malar Bone): is small and quadrangular, and is situated at the upper and
lateral part of the face: it forms the prominence of the cheek, part of the lateral wall and floor of the orbit,
and parts of the temporal and infratemporal fossæ. I
5. The Palatine Bone: is situated at the back part of the nasal cavity between the maxilla and the
pterygoid process of the sphenoid. It contributes to the walls of three cavities: the floor and lateral wall of
the nasal cavity, the roof of the mouth, and the floor of the orbit.
6. The Inferior Nasal Concha (Concha Nasalis Inferior; Inferior Turbinated Bone): extends
horizontally along the lateral wall of the nasal cavity.
7. The Vomer: is situated in the median plane, but its anterior portion is frequently bent to one or
other side. It is thin, somewhat quadrilateral in shape, and forms the hinder and lower part of the nasal
septum.
8. The Mandible (Lower Jaw): the largest and strongest bone of the face, serves for the reception of
the lower teeth. It consists of a curved, horizontal portion, the body, and two perpendicular portions, the
rami, which unite with the ends of the body nearly at right angles.
9. The Hyoid Bone: is shaped like a horseshoe, and is suspended from the tips of the styloid
processes of the temporal bones by the stylohyoid ligaments.
VERTEBRAL COLUMN, RIBS AND THE STERNUM
Ribs
Ribs (L. costae) are curved, flat bones that form most of the thoracic cage. There are three types of ribs:
 True (vertebrocostal) ribs (1st-7th ribs): They attach directly to the sternum through their own costal
cartilages.
 False (vertebrochondral) ribs (8th, 9th, and usually 10th ribs): Their cartilages are connected to the
cartilage of the rib above them; thus their connection with the sternum is indirect.
 Floating (vertebral, free) ribs (11th, 12th, and sometimes 10th ribs): The rudimentary cartilages of
these ribs do not connect even indirectly with the sternum; instead they end in the posterior
abdominal musculature.
Typical ribs (3rd-9th) have the following components:
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Head
Neck
Tubercle
Body (shaft)
Costal cartilages prolong the ribs anteriorly and contribute to the elasticity of the thoracic wall,
providing a flexible attachment for their anterior ends. The first 7 costal cartilages attach directly and
independently to the sternum; the 8th, 9th, and 10th articulate with the costal cartilages just superior to them,
forming a continuous, articulated, cartilaginous costal margin. The 11th and 12th costal cartilages form caps
on the anterior ends of the corresponding ribs and do not reach or attach to any other bone or cartilage.
Intercostal spaces separate the ribs and their costal cartilages from one another. The spaces are named
according to the rib forming the superior border of the space—for example, the 4th intercostal space lies
between ribs 4 and 5. There are 11 intercostal spaces and 11 intercostal nerves. Intercostal spaces are
occupied by intercostal muscles and membranes, and two sets (main and collateral) of intercostal blood
vessels and nerves, identified by the same number assigned to the space.
Sternum
The sternum (G. sternon, chest) is the long, flat bone that forms the middle of the anterior part of the
thoracic cage. It directly overlies and affords protection for mediastinal viscera in general and much of the
heart in particular. The sternum is commonly known as the breastbone and is divided into three areas, the
upper manubrium, the body, and the xiphoid process.
Manubrium: The manubrium (L. handle, as in the handle of a sword, with the sternal body forming the
blade) is a roughly trapezoidal bone. The manubrium is the widest and thickest of the three parts of the
sternum. The easily palpated concave center of the superior border of the manubrium is the jugular notch
(suprasternal notch). The other anatomical feature at that part of the sternum; the clavicular notches form
the sternoclavicular joints on both sides.
Body of the sternum: The body of the sternum is longer, narrower, and thinner than the manubrium.
Xiphoid process: (from xiphias “swordfish”) the smallest and most variable part of the sternum, is thin and
elongated.
Verterbral column
The vertebral column in an adult typically consists of 33 vertebrae arranged in five regions: 7
cervical, 12 thoracic, 5 lumbar, 5 sacral, and 4 coccygeal. The vertebrae gradually become larger as the
vertebral column descends to the sacrum and then become progressively smaller toward the apex of the
coccyx. The change in size is related to the fact that successive vertebrae bear increasing amounts of the
body's weight as the column descends. The vertebrae reach maximum size immediately superior to the
sacrum, which transfers the weight to the pelvic girdle at the sacroiliac joints.
The vertebral column is flexible because it consists of many relatively small bones, called vertebrae
(singular = vertebra), that are separated by resilient intervertebral (IV) discs.
Vertebrae vary in size and other characteristics from one region of the vertebral column to another, and to a
lesser degree within each region; however, their basic structure is the same.
A typical vertebra consists of a vertebral body, a vertebral arch, and seven processes.
The vertebral body is the more massive, roughly cylindrical, anterior part of the bone that gives strength to
the vertebral column and supports body weight. The size of the vertebral bodies increases as the column
descends as each bears progressively greater body weight.
The vertebral arch is posterior to the vertebral body and consists of two (right and left) pedicles and
laminae. The pedicles are short, stout cylindrical processes that project posteriorly from the vertebral body.
The vertebral arch and the posterior surface of the vertebral body form the walls of the vertebral foramen.
The succession of vertebral foramina in the articulated vertebral column forms the vertebral canal (spinal
canal), which contains the spinal cord and the roots of the spinal nerves that emerge from it.. Seven
processes arise from the vertebral arch of a typical vertebra:
 One median spinous process projects posteriorly from the vertebral arch at the junction of the
laminae.
 Two transverse processes project posterolaterally from the junctions of the pedicles and laminae.
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Four articular processes—two superior and two inferior—also arise from the junctions of the
pedicles and laminae, each bearing an articular surface (facet).
BONES OF THE UPPER LIMB & THE SHOULDER
Clavicle (Tr. Köprücük kemiği)
The clavicle (collar bone) connects the upper limb to the trunk. The shaft of the clavicle has a double curve
in a horizontal plane. Its medial half is convex anteriorly, and its sternal end is enlarged and triangular where
it articulates with the manubrium of the sternum at the sternoclavicular (SC) joint. Its lateral half is concave
anteriorly, and its acromial end is flat where it articulates with the acromion of the scapula at the
acromioclavicular (AC) joint. These curvatures increase the resilience of the clavicle and give it the
appearance of an elongated capital S.
The clavicle:
 increases the range of motion of the limb.
 affords protection to the neurovascular bundle supplying the upper limb.
 transmits shocks (traumatic impacts) from the upper limb to the axial skeleton.
Some prominent features of the superior and inferior surfaces of the clavicle:
Sternal end
Acromial end
Scapula (Tr. Kürek kemiği)
The scapula (shoulder blade) is a triangular flat bone that lies on the posterolateral aspect of the
thorax. The convex posterior surface of the scapula is unevenly divided by a thick projecting ridge of bone,
the spine of the scapula, into a small supraspinous fossa and a much larger infraspinous fossa. The concave
costal surface of most of the scapula forms a large subscapular fossa. The broad bony surfaces of the three
fossae provide attachments for fleshy muscles.
The spine continues laterally as the flat expanded acromion (G. akros, point), which forms the
subcutaneous point of the shoulder and articulates with the acromial end of the clavicle. Superolaterally, the
lateral surface of the scapula has a glenoid cavity (G. socket), which receives and articulates with the head
of the humerus at the glenohumeral joint. The glenoid cavity is a shallow, concave, oval fossa (L. fossa
ovalis), directed anterolaterally and slightly superiorly—that is considerably smaller than the ball (head of
the humerus) for which it serves as a socket. The beak-like coracoid process (G. korakōdés, like a crow's
beak) is superior to the glenoid cavity. The scapula has medial, lateral, and superior borders and superior,
lateral, and inferior angles. The glenoid cavity is the primary feature of the head. The shallow constriction
between the head and the body defines the neck of the scapula. The superior border of the scapula is
marked by the suprascapular notch, which is located where the superior border joins the base of the coracoid
process.
Humerus
The humerus (arm bone), the largest bone in the upper limb, articulates with the scapula at the
glenohumeral joint and the radius and ulna at the elbow joint. The proximal end of the humerus has a head,
surgical and anatomical necks, and greater and lesser tubercles. The spherical head of the humerus
articulates with the glenoid cavity of the scapula. The surgical neck of the humerus, a common site of
fracture, is the narrow part distal to the head and tubercles.
The shaft of the humerus has two prominent features: the deltoid tuberosity laterally, and the oblique
radial groove posteriorly. The inferior end of the humeral shaft widens as the sharp medial and lateral
supraepicondylar (supracondylar) ridges form and then end distally in the especially prominent medial
epicondyle and the lateral epicondyle, providing for muscle attachment. The distal end of the humerus—
including the trochlea; the capitulum; and the olecranon, coronoid, and radial fossae—makes up the condyle
of the humerus.
Bones of Forearm
The two forearm bones serve together to form the second unit of an articulated mobile strut (the first
unit being the humerus), with a mobile base formed by the shoulder, that positions the hand.
The ulna is the stabilizing bone of the forearm and is the medial and longer of the two forearm
bones. Its more massive proximal end is specialized for articulation with the humerus proximally and the
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head of the radius laterally. For articulation with the humerus, the ulna has two prominent projections: (1)
the olecranon, which projects proximally from its posterior aspect (forming the point of the elbow) and
serves as a short lever for extension of the elbow, and (2) the coronoid process, which projects anteriorly.
The radius is the lateral and shorter of the two forearm bones. Its proximal end includes a short head,
neck, and medially directed tuberosity. Proximally, the smooth superior aspect of the discoid head of the
radius is concave for articulation with the capitulum of the humerus during flexion and extension of the
elbow joint. The head also articulates peripherally with the radial notch of the ulna; thus the head is covered
with articular cartilage. The neck of the radius is a constriction distal to the head. The shaft of the radius, in
contrast to that of the ulna, gradually enlarges as it passes distally. The distal end of the radius is essentially
four sided when sectioned transversely. Its medial aspect forms a concavity, the ulnar notch which
accommodates the head of the ulna. Its lateral aspect becomes increasingly ridge-like, terminating distally in
the radial styloid process.
Bones of the hand
The wrist, or carpus, is composed of eight carpal bones (carpals) arranged in proximal and distal rows of
four: The proximal surfaces of the distal row of carpals articulate with the proximal row of carpals, and their
distal surfaces articulate with the metacarpals. The metacarpus forms the skeleton of the palm of the hand
between the carpus and the phalanges. It is composed of five metacarpal bones (metacarpals). Each
metacarpal consists of a base, shaft, and head. The proximal bases of the metacarpals articulate with the
carpal bones, and the distal heads of the metacarpals articulate with the proximal phalanges and form the
knuckles. Each digit has three phalanges except for the first (the thumb), which has only two. Each phalanx
has a base proximally, a shaft (body) and a head distally.
BONES OF THE LOWER LIMB & THE PELVIC GRIDLE
The skeleton of the lower limb (inferior appendicular skeleton) may be divided into two functional
components: the pelvic girdle and the bones of the free lower limb. The pelvic girdle is a ring of bones that
connects the vertebral column to the two femurs. The primary functions of the pelvic girdle are bearing and
transfer of weight; secondary functions include protection and support of abdominopelvic viscera and
housing and attachment for structures of the genital and urinary systems.
In the mature individual, the pelvic girdle is formed by three bones:
 Right and left hip bones (coxal bones; pelvic bones): large, irregularly shaped bones, each of which
develops from the fusion of three bones, the ilium, ischium, and pubis.
 Sacrum: formed by the fusion of five, originally separate, sacral vertebrae.
Male and female pelves are distinct. The characteristic features of the normal (gynecoid) female pelvis
reflect the fact that the fetus must traverse the pelvic canal during childbirth. Because atypical female pelves
may not be conducive to a vaginal birth, determination of the pelvic diameters is of clinical importance.
Hip Bone
The mature hip bone (L. os coxae) is the large, flat pelvic bone formed by the fusion of three primary
bones—ilium, ischium, and pubis.
The ilium is the superior, fan-shaped part of the hip bone. The ala, or wing, of the ilium represents
the spread of the fan, and the body of the ilium, the handle of the fan. On its external aspect, the body
participates in formation of the acetabulum. The iliac crest, the rim of the fan, has a curve that follows the
contour of the ala between the anterior and the posterior superior iliac spines. The anteromedial concave
surface of the ala forms the iliac fossa.
The ischium has a body and ramus (L. branch). The body of the ischium helps form the acetabulum
and the ramus of the ischium forms part of the obturator foramen. The large posteroinferior protuberance of
the ischium is the ischial tuberosity. The small pointed posteromedial projection near the junction of the
ramus and body is the ischial spine.
The pubis is an angulated bone with a superior ramus, which helps form the acetabulum, and an
inferior ramus, which helps form the obturator foramen.
The acetabulum (L., shallow vinegar cup) is the large cupshaped cavity or socket on the lateral aspect of the
hip bone that articulates with the head of the femur to form the hip joint. All three primary bones forming the
hip bone contribute to the formation of the acetabulum.
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Sacrum
The wedged-shaped sacrum (L. sacred) is usually composed of five fused sacral vertebrae in adults. It
is located between the hip bones and forms the roof and posterosuperior wall of the posterior half of the
pelvic cavity. The sacral canal is the continuation of the vertebral canal in the sacrum.
Coccyx
The coccyx (tail bone) is a small triangular bone that is usually formed by fusion of the four
rudimentary coccygeal vertebrae. The coccyx is the remnant of the skeleton of the embryonic tail-like caudal
eminence. The coccyx does not participate with the other vertebrae in support of the body weight when
standing; however, when sitting it may flex anteriorly somewhat, indicating that it is receiving some weight.
The coccyx provides attachments for muscles.
Femur
The femur is the longest and heaviest bone in the body. It transmits body weight from the hip bone
to the tibia when a person is standing. The femur consists of a shaft (body) and two ends, superior or
proximal and inferior or distal. The superior (proximal) end of the femur consists of a head, neck, and two
trochanters (greater and lesser). The neck of the femur is trapezoidal, with its narrow end supporting the
head and its broader base being continuous with the shaft. The greater trochanter is a large, laterally placed
bony mass that projects superiorly and posteriorly where the neck joins the femoral shaft. The medial and
lateral femoral condyles make up nearly the entire inferior (distal) end of the femur.
Bones of the Leg
The tibia and fibula are the bones of the leg. The tibia articulates with the condyles of the femur
superiorly and the talus inferiorly and in so doing transmits the body's weight. The fibula mainly functions as
an attachment for muscles, but it is also important for the stability of the ankle joint.
Tibia
Located on the anteromedial side of the leg, nearly parallel to the fibula, the tibia (shin bone) is the
second largest bone in the body. It flares outward at both ends to provide an increased area for articulation
and weight transfer. The superior (proximal) end widens to form medial and lateral condyles that overhang
the shaft medially, laterally, and posteriorly, forming a relatively flat superior articular surface, or tibial
plateau. This plateau consists of two smooth articular surfaces that articulate with the large condyles of the
femur. The tubercles fit into the intercondylar fossa between the femoral condyles.
The anterior border of the tibia is the most prominent border. It and the adjacent medial surface are
subcutaneous throughout their lengths and are commonly known as the “shin”; their periosteal covering and
overlying skin are vulnerable to bruising. At the superior end of the anterior border, a broad, tibial tuberosity
provides distal attachment for the patellar ligament, which stretches between the inferior margin of the
patella and the tibial tuberosity. The inferior surface of the shaft and the lateral surface of the medial
malleolus articulate with the talus. The interosseous border of the tibia is sharp where it gives attachment to
the interosseous membrane that unites the two leg bones. Inferiorly, the sharp border is replaced by a groove,
the fibular notch that accommodates and provides fibrous attachment to the distal end of the fibula.
Fibula
The slender fibula lies posterolateral to the tibia and is firmly attached to it by the tibiofibular
syndesmosis, which includes the interosseous membrane. The fibula has no function in weight-bearing. It
serves mainly for muscle attachment. The distal end enlarges and is prolonged as the lateral malleolus. The
proximal end of the fibula consists of an enlarged head superior to a small neck. The head has a pointed
apex.
Bones of the foot
The bones of the foot include the tarsus, metatarsus, and phalanges. There are 7 tarsal bones, 5
metatarsal bones, and 14 phalanges. The calcaneus (L., heel bone) is the largest and strongest bone in the
foot. When standing, the calcaneus transmits the majority of the body's weight from the talus to the ground.
The navicular (L., little ship) is a flattened, boat-shaped bone located between the head of the talus
posteriorly and the three cuneiforms anteriorly. The cuboid, approximately cubical in shape, is the most
lateral bone in the distal row of the tarsus. The three cuneiform bones are the medial (1st), intermediate
(2nd), and lateral (3rd). The metatarsus (anterior or distal foot, forefoot—) consists of five metatarsals that
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are numbered from the medial side of the foot. The 14 phalanges are as follows: the 1st digit (great toe) has
2 phalanges (proximal and distal); the other four digits have 3 phalanges each: proximal, middle, and distal.
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