Section One
Bones

Ⅰ．The Shape and Architecture of Bones

Bones （骨） are classified by shape as long，short，flat and irregular bones（Figure 2.2）．Each long bone has a shaft or body and two ends．The shaft has a cavity which is known as medullary cavity．The ends are wider and known as epiphyses （骺） ，which are composed of cancellous or spongy bones．The shaft is connected with the epiphysis by an epiphysial cartilage，which elongates bones．After the ossification of the epiphysial cartilage in adult，it becomes the epiphysial line（Figure 2.3）．Arm，forearm，thigh and leg bones are long bones．Short bones are cuboidal．They can bear stronger pressure．The carpal and tarsals bones are short bones．Flat bones are plate-like and form the cranial，thoracic and pelvic cavities．The sternum，ribs and some of the cranial bones are flat bones．Irregular bones are greatly varied in shape，carrying out different functions．Some of the facial bones，the vertebrae，and the hip bones are irregular bones．

Living bones consist of bony substance，bone marrow and periosteum，and are abundant in blood vessels and nerves supply（Figure 2.4）．The bony substance （骨质） include compact or dense bone and cancellous or spongy bone．The compact bone （骨密质） is also called cortical bone，forms the exterior of bones．It is dense and provides strength for weighbearing．Compact bone makes up 80％ of the human skeleton．The spongy bone （骨松质） distributes in the interior of bones，and consists of a lot of trabeculae，which arrange into an expanded meshwork like the sponge．The trabeculae are arranged in line of the pressure and of tension． Bone marrow （骨髓） is filled in the medullary cavities and with spaces in cancellous bone．There are two types of bone marrow，red and yellow．The red marrow can produce blood cells．The yellow marrow comprises lots of fat and makes no blood cells．In infants and young children，red marrow is found in many bones．By the sixth year，the red marrow is gradually replaced by yellow marrow．In adults，it is found mainly in the ribs，sternum，vertebrae and pelvic bones．When blood is severely lost，some yellow marrow reverts to red marrow and begins to produce blood cells． Periosteum （骨膜） is a membrane that invests the outer surface of all bones except the articular part．It abounds with blood vessels，nerves and osteoblasts，and plays important roles in the nutrition，growth and regeneration of the bones．Osteoblasts are bone-forming cells，which secrete collagen．The collagen forms a network of fibers called osteoid，which mineralizes to become bone．Osteoblasts also are immature bone cells，and will finally become trapped the mineral deposits to become mature bone cells known as osteocytes．Bone contains another cells called osteoclasts，which dissolve bone by secreting enzymes．Together，osteoblasts and osteoclasts alter bone density，and are responsible for bone development．

Ⅱ．The Chemical Composition and Physical Properties of Bones

The chemical composition of living bones is composed of organic and inorganic components．The organic materials （有机质） mainly contain collagen and mucopolysaccharide，and make bones resilient and tough（Figure 2.5）；the inorganic materials （无机质） are mainly calcium phosphate，which give bones hardness and rigidity．The physical properties of the bones depend on the chemical components．The ratio between the organic and inorganic materials changes as we grow older．In infant and child，the organic components are relatively more than those in adult，so their bones are softer，and easy to be deformed．In adults，the ratio is about 3 to 7，which gives bones a great hardness and strong resilience．Older people comparatively have more inorganic components and thus bone fractures often occur．Bones can be affected both by internal and external environmental factors，such as age，sex，stature，habitude，health，diet，race，genetic and endocrinological conditions．Exercise facilitates the healthy development and growth of bones，and makes them strong．Lacking exercise over a long time can lead weak bones．

Ⅲ．Classification of Bones

There are 206 distinct bones in the skeleton of the adult．They are divided into bones of the trunk，limbs and skull．

Bones of the trunk （躯干骨） Theyarecomposedof26 vertebrae （椎骨） ，24 ribs （肋骨） anda sternum （胸骨） ，taking part in formation of the vertebral column，thorax and pelvis（Figure 2.6）．The 26 vertebrae comprise 7 cervical，12 thoracic and 5 lumbar vertebrae，1 sacrum and 1 coccyx from superior to inferior．A typical vertebra consists of an anterior vertebralbody （椎体） and a posterior vertebralarch （椎 弓） ，which encloses the vertebralforamen （椎孔） （Figure 2.7）．The vertebral foramina of all vertebrae constitute the vertebral canal of spinal canal which lodges the spinal cord．The vertebral body is cylindrical and supports the weight of body．The vertebral arch is formed by a pair of pedicles and a pair of laminae，and sends seven processes，which include four articular，two transverse，and one spinous processes．The articular processes project obliquely upwards and downwards from the junctions of the pedicles and laminae．The transverse processes project laterally from the junction of the pedicle and lamina．The spinous processes are directed backward from the junction of laminae in the posterior midline．Between adjacent vertebrae on each side has an intervertebralforamen （椎间孔） through which a spinal nerve passes from the spinal cord（Figure 2.8）．The vertebrae are not all the same．The cervical vertebrae are the smallest．Their transverse process have transverse foramina for transmission of the vertebral artery and vein．The spinous processes are short and bifurcated（except C1 and C7）．The first cervical is called atlas （寰椎） and has no body nor spine．The second cervical has a toothlike projection known as dens on the superior surface of the body and is called axis （枢椎） ．The seventh is called vertebraprominens （隆椎） as it has a long spinous process．The thoracic vertebrae are larger than the cervical．They have the costal facets on their bodies and transverse processes for the articulation of the ribs．The lumbar vertebrae are the largest and strongest of all．The sacrum （骶骨） consists of five sacral vertebrae，fused together and forming one firm bone in the adult．It is a triangular bone between two hip bones．Its anterior surface is concave，and has four pairs of anterior sacral foramina for transmission of the anterior divisions of the sacral nerves．Similarly，its dorsal surface has four pairs of posterior sacral foramina for transmission of the posterior divisions of the sacral nerves．The coccyx （尾骨） is an appendage of the sacrum，and consists of four coccygeal bones fused together in the adult．

There are twelve ribs on each side；the upper seven are true ribs （真肋） connected with the sternum by their own cartilages（Figure 2.6）．The remaining five are false ribs （假肋） ，three of them are connected indirectly with the sternum by their cartilages，being attached each to the one above it．The last two ribs have no sternal attachment，ending in the abdominal muscles，and are termed floating ribs （浮肋） ．A typical rib is a long twisted bone，which has an anterior extremity，a posterior extremity，and an intervening body or shaft．The posterior extremity consists of a head，neck and tubercle．The body bends sharply forward to form the angle．The anterior extremity joints the corresponding costal cartilage（Figure 2.9）．

The sternum （胸骨） is in the middle line in the front of the chest（Figure 2.6）．It is likened to a sword—the upper part is called the manubrium （柄） ，the middle part called body （体） ，and the lower part called xiphoid process （剑突） ．

Bones of limbs （上肢骨） They include the upper and lower limb bones．Bones of the upper limb consist of the bones of the shoulder girdle（clavicle and scapula），the bone of upper arm （humerus），the bones of forearm （radius and ulna）， and the bones of hand （carpal bones， metacarpal bones and phalanges）．The clavicle （锁骨， Latin . little key ） is a doubly curved short bone that connects the arm（upper limb）to the body（trunk），extending almost horizontally across the root of the neck（Figure 2.10）．The scapula （肩胛骨） is a flat triangular bone，which lies on the posterolateral aspect of the thorax（Figure 2.11）．It connects the clavicle to the humerus．The scapula is traversed at the back by a ridge，the spine of the scapula （肩胛冈） ，which ends in the acromion （肩峰） ．Its lateral angle presents a shallow glenoid cavity （关节盂） for articulation with the head of the humerus．The bone of upper arm is humerus （肱骨） （Figure 2.12），which is a long cylindrical bone．Its upper head is round and directed upwards and inwards．Its shaft（body）is circular in the upper part and fattened in its lower part．Its lower end is also flattened，and has two projections called condyles，the medial and the lateral．At the back，between the two condyles，is an olecranon fossa，into which the olecranon process of the ulna fits when the forearm is extended；in front of it，there is a smaller coronoid fossa，into which the coronoid process of the ulna fits when the forearm is flexed．An articulating surface on the inner side for the ulna is called the trochlea，and that for the radius on the outer side is called the capitulum．The bones of the forearm are ulna （尺骨） and radius （桡骨） （Figure 2.13）．The ulna is the medial bone of the forearm，and its upper head has two processes，the coronoid and the olecranon．Between the two processes is the trochlear notch．The lower end of the ulnar projects downwards and inwards to form the styloid process．The radius is the lateral bone of the forearm，and its upper head is small and button-shaped．Its lower end projects downwards and outwards to form the styloid process．The styloid process of the radius extends 1 cm further than the styloid process of the ulnar．The bones of hand include the carpal bones （腕骨）， metacarpal bones （掌骨） and phalanges （指骨） （Figure 2.14）．There are eight small carpal bones form the wrist，two rows of four bones each．From the thumb，the bones of the proximal row are the scaphoid，lunate，triquetral and pisiform bones；the distal row are the trapezium，trapezoid，capitate and hamate bones．Five metacarpal bones form the palm，and numbered from the first to the fifth from the thumb to the little fingers．There are fourteen phalanges，three in each finger and two in the thumb．

Bonesofthelowerlimb （下肢骨） consist of the pelvic girdle（hip bone），the bone of thigh（femur），patella，the bones of leg（tibia and fibula）and the bones of foot（tarsal，metatarsal bones and phalanges）．Two hip bones form most part of the pelvis．In the child，a hipbone （髋骨） is composed of three parts：the superior ilium （髂骨） ，the posteroinferior ischium （坐骨） ，and the anteroinferior pubis （耻骨） （Figure 2.15）．In the adults，the three bones are united at the lateral fossa called the acetabulum （髋臼） which is the socket for the head of femur．The obturatorforamen （闭孔） lies anteroinferior to the acetabulum，and is a large opening between the ischium and pubis as a passageway for the obturator artery，vein and nerve．The superior thick border of the ilium is called the iliaccrest （髂嵴） ．The lowest part of the ischium is a rough prominence called the ischialtuberosity （坐骨结节） ．This is the part we sit on．The pubis is joined to its fellow of the opposite side by a plate of fibro-cartilage，forming a joint called the symphysispubis （耻骨联合） ．The bone of thigh is the femur （股骨） （Figure 2.16），which is the longest and strongest bone ofhuman skeleton．Its length is about 1/4 of a person's height．The femur is divided into one body and two ends．The upper end contains a head and a neck．The head creates about 2/3 of a sphere，and is directed upwards，inwards，and a little forwards．It articulates with the acetabulum of the hip bone to form the hip joint．The neck of the femur is a constricted part connecting the head and the body．The lower end of the femur is flattened；it has two projections，called medial and lateralcondyles （内侧髁、外 侧髁） ．The two condyles articulate with the tibia below and the patella anteriorly．The bones of the leg are the tibia （胫骨） and fibula （腓骨） （Figure 2.17）．The tibia is the medial and larger bone；its upper end is expanded into two eminence，the medial and lateral condyles．Its lower end projects downwards to form the medialmalleolus （内踝） ．The fibula is parallel with the tibia on its outer side．Its upper end is slightly expanded to form the head．The neck is a narrow part below the head．The common peroneal nerve wraps around the neck of the fibula．The lower end of the fibula is termed the lateralmalleolus （外踝） ．The patella （髌骨） locates at front of the knee-joint（Figure 2.16）；it is a sesamoid bone developed in the tendons of the extensor quadriceps muscles．There are twenty-six bones in the foot（Figure 2.18）．Seven tarsalbones （跗骨） are connected superiorly to the tibia and fibula to form the ankle joint．Among them，the talus and calcaneus form the hindfoot，the five irregular bones of the midfoot are the cuboid，navicular，and three cuneiform bones．There are five metatarsalbones （跖骨） ，which articulate at their bases with the tarsal bones，and at their heads with the bones of the toes．There are fourteen phalanges （趾骨） ，arranged as in the fingers．

Skull （颅骨） It is divided into the cranial bones and facial bones（Figure 2.19）．There are eight cranial bones，which primarily form the cranial cavity．The cranial bones include one frontal bone （额骨） ，one occipital bone （枕骨） ，one ethmoid bone （筛骨） ，one sphenoid bone （蝶骨） ，two parietal bones （顶骨） and two temporal bones （颞骨） ．

The frontal bone corresponds with the region of the forehead，forming the upper and fore part of the skull．Its shape is similar to a shell．It contains a pair of frontal sinuses which are immediately above and between orbits．The two parietal bones unite and form the sides and roof of the skull．Each bone is quadrilateral in form．The temporal are situated in the lower sides and base of the skull．It is divided into the squamous part，tympanic part and petrous part with the external acoustic pore as the center． The squamous part is anterosuperior to the external acoustic pore，and extends the zygomatic process that joints the zygomatic bone to form the zygomatic arch．The tympanic part is a curved plate of bone surrounding the external acoustic meatus．The petrous part of the temporal bone is a pyramid shaped mass of bone between the sphenoid and occipital bones．The inner ear and primary part of the middle ear are located in the petrous part．The mastoid process is a conical projection from the base of the petrous part，felt behind the earlobe．The styloid process is a long slender projection behind the mastoid process．The two processes provide points of attachment for muscles and ligaments．The occipital forms the back and base of the skull．It has a large opening called foramen magnum （枕骨大孔） ，which transmits the spinal cord．The ethmoid lies between the orbits，at the roof of the nose．It looks like a Chinese character“巾”from the anterior view．The ethmoid bone is divided into the cribriform plate，perpendicular plate，and labyrinths．The cribriform plate，forming the roof of the nose，is a horizontal plate of bone through which the olfactory nerves from the nasal epithelium pass to the brain．The perpendicular plate descends from the cribriform plate，and consists of the superior part of the nasal septum．The labyrinths，located at either side of the perpendicular plate，are two lateral masses which contain many cellular cavities called the ethmoid sinuses．A superior nasal concha and a middle nasal concha，two thin scroll shaped plates，project from the medial surface of each labyrinth．The sphenoid lies at the middle of the base of the skull in front of the occipital and behind the frontal bones．Its shape somewhat resembles that of a butterfly or bat with its wings extended．The sphenoid bone is divided into a body，a pair of greater wings，a pair of lesser wings，and a pair of pterygoid processes．The body is the central portion that contains two hollow cavities named the sphenoidal sinuses．The superior surface of the body as a depression，the hypophyseal fossa or sella turcica，in which the pituitary gland lies．The greater wings extend laterally from the sides of the body，while the lesser wings spread outwards from the anterosuperior part of the body．The two wings form the middle cranial floor．The pterygoid processes project downwards from the body，and form the posterior part oflateral wall of the nasal cavity．There are fifteen facial bones，which mainly form the framework of the face．The facial bones include two maxillae （上颌骨） ，two zygomatic bones （颧骨） ，two nasal bones （鼻骨） ，two lacrimal bones （泪骨） ，two palate bones （腭骨） ，two inferior nasal conchae （下鼻甲） ，one vomer （犁骨） ，one mandible （下颌骨） and one hyoid bone （舌骨） ．The maxilla is situated at the middle of the face，and mainly forms the upper jaw，the socket for the upper teeth and the greater portion of the hard palate．It is divided into a body and four processes．The body contains a large cavity termed the maxillary sinus．The alveolar process descends from the body，and is a bony socket for the upper teeth．The zygomatic bones form the projection of the cheek，part of the outer and lower margin of the orbit，and part of the zygomatic arch．The nasal bones are situated between the orbits，and form a ridge known as the bridge of the nose．The lacrimal bones are two very tiny delicate bones which lie behind the frontal process of the maxilla and form the anterior part of the medial wall of the orbit．The palate bones lie at the back of the nasal cavity and consist of the posterior part of the bone palate．The inferior nasal conchae are small curved bones along the lateral wall of the nasal cavity．The vomer is a trapezoid bone which separates the two nostrils．The mandible forms the lower jaw．It is divided into a body and two rami．The body is a curved central part．The superior part of the body is a socket for the lower teeth．The anterolateral surface of the body has a pair of openings named the mental foramen that transmits the mental nerve and blood vessels．The mandibular foramen is located on the medial surface of the each ramus，and is the entrance of the mandibular canal that ends at the mental foramen．The inferior alveolar nerve enters the mandibular canal through the mandibular foramen．The superior part of the ramus has two processes，the anterior coronoid process and the posterior condylar process．The condylar process joints the temporal bone to form the temporomandibular joint．The hyoid bone is situated in the neck between the mandible and larynx．

The bones of body are summarized in Table 2.1，2.2 and 2.3．