Bones provide support for the body, enable body motion, and protect the various organs of the body.
Fig. 1-2. Compact and spongy bones, medullary cavity.
In the longitudinal plane of a long bone (Fig. 1-5), two epiphyses and one diaphysis are identifiable. The epiphysis consists of (outer) compact bone and (inner) spongy bone. The spongy bone is much more complicated with the trabeculae than in the figure above. The diaphysis is composed of (outer) compact bone and (inner) medullary cavity (Fig. 3-47).
The medullary cavity is filled with the bone marrow. Before broiling the T-bone, we can see the bone marrow that is red.
The periosteum is a membrane that covers the outer surface of bone, except at the synovial joint where bone is covered by the articular cartilage (Fig. 2-32).
A long bone is the humerus (Fig. 1-22). A cup-shaped short bone is the carpal bone (Fig. 1-25). A flat bone is the calvaria covering the brain (Fig. 13-43) (Fig. 15-8). An irregular bone is the vertebra (Fig. 1-13).
In the human body at birth, there are over 270 bones, but some of these fuse together during development, leaving a total of 206 separate bones in the adult. Among them, 80 bones are axial skeleton, 126 bones are appendicular skeleton. (The authors do not ask students to memorize such numbers of bones. Everyone knows numbers are easily forgettable.)
Among the numerous bones and their complicated structures, only what are related with other systems (e.g., muscular system) will be briefly introduced.
< Axial skeleton >
The individual skull bones are held together by sutures (Fig. 2-2). For a representative example, the big four bones (frontal, parietal, temporal, and occipital bones) are connected by the sutures.
Fig. 1-8. Pterion above zygomatic arch.
For another example, the frontal, parietal, temporal, and sphenoid bones collectively configurate H-shaped sutures known as the pterion. The pterion is located above the palpable zygomatic arch (Fig. 1-11) (Fig. 3-13).
The thin pterion is protected by the temporal muscle that covers it (Fig. 3-13). However, the pterion can be fractured to yield the fatal hemorrhage (Fig. 13-43).
Fig. 1-10. Superciliary arch, supraorbital notch or foramen.
Superciliary arch inside the eyebrow is a part of the frontal bone (Fig. 1-7). The male has the more protruding superciliary arch than the female counterpart.
Supraorbital notch, another part of the frontal bone, is to be noticed in one’s own body. Unless one is able to palpate the supraorbital notch, one has the supraorbital foramen (Fig. 13-69). That is simply a variation regardless of function.
Fig. 1-11. Temporal bone.
The temporal bone participates in the lateral wall of the skull (Fig. 1-8). Its process articulates with the zygomatic bone to form the zygomatic arch (Fig. 1-8). Posteroinferior part is the mastoid process (Fig. 3-16) and styloid process (Fig. 3-19). The mastoid process is palpable posteroinferior to the auricle (Fig. 14-29) in one’s body. But the styloid process is not palpable unlike the styloid processes of the radius and ulna (Fig. 1-23).
Along with the occipital bone, the temporal bone also participate in the skull base to support brain and contains the ear structures (Fig. 14-29) (Fig. 14-36).
Two parts of the skull are the neurocranium and the facial skeleton. The neurocranium includes calvaria (skull cap) under the scalp (Fig. 15-8). The facial skeleton includes the mandible as its largest bone.
The temporomandibular joint between the temporal bone (Fig. 1-7) above and the mandible below is a synovial joint (Fig. 2-43).
Fig. 1-13. Vertebra.
A typical vertebra consists of two parts: vertebral body and vertebral arch. Together, these enclose the vertebral foramen, which contains the spinal cord (Fig. 13-40).
From the vertebral arch of a vertebra, seven processes project; prominent ones are a spinous process that is easily palpable and two transverse processes.
Fig. 1-14. Intervertebral foramen.
The vertebral arches of neighboring vertebrae form an intervertebral foramen that conducts the spinal nerve (Fig. 13-84).
The vertebral column is composed of several vertebrate. Basically, the cervical vertebrae is associated with neck, the thoracic vertebrae with thorax, the lumbar vertebrae with abdomen, the sacrum and coccyx with pelvis and perineum.
The vertebral column of a fetus is convex backward; think of the crouching posture of a fetus (Fig. 2-28). After birth, the cervical vertebrae and the lumbar vertebrae become convex forward.
The curvature of lumbar vertebrae is used as an excuse for a lazy anatomist’s potbelly.
Fig. 1-17. Sacrum.
The sacrum is formed by the fusing of five sacral vertebrae. In the lower sacral vertebrae, vertebral arches (Fig. 1-13) are not formed, resulting in the sacral hiatus that is to be touched by oneself. Above the sacral hiatus, the spinous processes (Fig. 1-14) are fused to form the median sacral crest that is also palpable.
The thoracic wall consists of thoracic vertebrae, ribs and sternum. R1–R7 separately contact the sternum while R8–R10 contact the sternum by way of R7 (Fig. 13-98). R11–R12 do not contact the sternum (Fig. 6-3).
The sternum is divided into manubrium, body, and xiphoid process (Fig. 3-22). Touch your protruding sternal angle between the manubrium and body (Fig. 10-5). Then you are able to touch R2 that is at the same level. Touch your xiphoid process that is slightly depressed.
< Appendicular skeleton >
Palpate the whole length of curved clavicle that is the only long bone in the body that lies horizontally (Fig. 3-40).
Fig. 1-21. Scapula.
The clavicle articulates with the acromion. We can touch the acromion that is the lateral end of the spine of scapula. Moreover, we can touch but also the coracoid process that is the another process of scapula just below the clavicle.
The supraglenoid tubercle (Fig. 3-48) and infraglenoid tubercle (Fig. 3-51) are small projections superior and inferior to the glenoid cavity, respectively.
The spine of scapula and medial border of scapula are palpable. The spine is border between the supraspinous fossa and infraspinous fossa. The anterior side of scapula has a broad concavity called the subscapular fossa.
Fig. 1-22. Humerus.
The head of humerus (ball) encounters the glenoid cavity (socket) to form the shoulder joint (ball and socket joint) (Fig. 2-51).
The greater and lesser tubercles and the deltoid tuberosity are structures, to which muscles are attached (Fig. 3-40) (Fig. 3-42).
At the distal end of humerus, touch your medial and lateral epicondyles that do not move during elbow flexion and extension (Fig. 2-19).
Fig. 1-23. Radius, ulna.
A large eminence of the ulna behind the elbow is the olecranon. Touch your olecranon that moves during elbow flexion and extension (Fig. 2-19).
At the distal end of ulna, its head and styloid process are located. In anatomical position, touch your styloid process of ulna.
At the proximal and distal ends of radius, its head and styloid process exist, respectively (Fig. 1-23). Touch your head of radius during pronation and supination (Fig. 2-46) just below the lateral epicondyle of humerus (Fig. 1-22).
Everyone is confused by the names of carpal bones. The best sentences to commit to memory are introduced in the cartoon.
Fig. 1-26. Carpal bones.
The carpal bones are concave anteriorly, so that the trapezium, scaphoid at lateral side and the hamate, pisiform at medial side are easily palpated through the anterior skin of wrist.
Fig. 1-27. Bones of hand.
In this book, the metacarpal bones and the phalanges are depicted as the 5 lines and 14 squares to distinguish them from one another (Fig. 3-55) (Fig. 3-59). Such depiction is also applied for the illustration of the metatarsal bones and phalanges in the foot (Fig. 1-47).
Make a fist, and you will notice that major knuckles are the heads of 1st and 2nd metacarpal bones.
Human being’s hand is clearly different from the foot (Fig. 2-25).
The clavicle and scapula are affiliated with the upper limb bones, whereas the hip bone with the lower limb bones. These bones connect trunk with the upper and lower limbs.
The hip bone consists of the ilium, ischium, and pubis.
Fig. 1-31. Hip bone.
Regarding the ilium, you can palpate the entire length of the iliac crest that stretches from the anterior superior iliac spine (Fig. 7-3) to the posterior superior iliac spine.
Three components of the hip bone come together to form the acetabulum (Fig. 2-52). The ischium and pubis constitute the obturator foramen. The obturator foramen is named because this foramen is obstructed by a membrane with a small passage for the obturator nerve (Fig. 13-100) and so on.
When sitting, the weight is placed upon the ischial tuberosity.
The gluteus maximus provides cover for the ischial tuberosity in the upright posture (Fig. 3-71); however, it does not in the seated posture.
Fig. 1-34. Pubis, ischium.
The pubic tubercle is a palpable projecting structure of the pubis. In male, the spermatic cord including the ductus deferens (Fig. 7-2) is palpable on the pubic tubercle.
Fig. 1-35. Greater and lesser pelvises.
The right and left hip bones, sacrum, and coccyx are assembled to make up the pelvic skeleton. Space inside the pelvic skeleton are the greater and lesser pelvises. The greater pelvis falls into the abdominal cavity. In other words, the greater pelvis contains abdominal organs such as cecum, descending colon (Fig. 4-33). The lesser pelvis is divided into the pelvic cavity and the perineum by the pelvic diaphragm (Fig. 3-64).
The superior and inferior apertures of the lesser pelvis are the pelvic inlet and outlet, respectively. During delivery (Fig. 8-42), the baby enters the lesser pelvis through the pelvic inlet, and then exits through the pelvic outlet.
A remarkable thing is that the pelvic inlet and outlet of the female are larger than those of the male. In addition, the pelvic inlet and outlet of the female are not distant from each other.
Fig. 1-37. Pelvic inlet.
The pelvic inlet that is close to a circle is outlined by the pubis, ilium (Fig. 1-31), and sacrum (Fig. 1-17). The pubic symphysis (cartilaginous joint) (Fig. 2-7) and sacroiliac joint (synovial joint) (Fig. 2-32) shift during a delivery, or due to a terrible trauma.
Fig. 1-38. Pelvic outlet.
The diamond-shaped pelvic outlet is composed of the urogenital and anal triangles. While the urogenital triangle is bordered by the pubis and ischium (Fig. 1-34), the anal triangle is bordered by the sacrotuberous ligament (Fig. 3-63) and coccyx (Fig. 1-17). The boundary between the two triangles is an imaginary line between the bilateral ischial tuberosities (Fig. 1-31).
Fig. 1-39. Lesser pelvis in anatomical position.
Some may think that the urogenital and anal triangles are located on the same plane (Fig. 1-38). However, the two triangles lie on different planes. Touch yours in anatomical position (Fig. 2-14).
Human has the lower limb bones that are specialized for two-legged locomotion.
Fig. 1-41. Femur.
The head of femur articulates with the acetabulum of hip bone (Fig. 1-31) forming the hip joint (Fig. 2-52). Meanwhile, the medial and lateral condyles of femur articulates with the medial and lateral condyles of tibia (Fig. 1-43) forming the knee joint (Fig. 2-37).
The posterior surface of femur involves the muscle attachments: the gluteal tuberosity (Fig. 3-71), the lateral and medial lips of linea aspera (Fig. 3-67) (Fig. 3-69).
Touch your greater trochanter, the lateral prominent of the femur.
Fig. 1-43. Femur, patella, tibia, fibula.
In the leg, the tibia is larger and stronger than the fibula (Fig. 3-76). The fibula is not in touch with the femur, so the bone does not contribute to the knee joint; but the fibula contributes to the ankle joint together with the tibia (Fig. 1-48).
Touch the medial and lateral condyles of tibia that move during knee flexion and extension (Fig. 2-27) unlike the medial and lateral condyles of femur. Other palpable structures of the tibia are the tibial tuberosity (Fig. 3-67), medial surface (Fig. 3-76), and medial malleolus. Palpable structures of the fibula are the head and lateral malleolus (Fig. 3-77).
When you kneel, the patella does not hit the floor. It is the tibial tuberosity that does.
The medial surface of the tibia is not covered by muscles (Fig. 1-43) (Fig. 3-76). Even in an obese person, the medial surface is palpable over the skin and minimal subcutaneous tissue. Thus, the medial surface is vulnerable to impact from outside.
The birds and four-footed animals walk on their tiptoes. Their knee joints are commonly hidden close to the trunk.
Fig. 1-47. Bones of foot.
The tarsal bones, metatarsal bones, and phalanges of foot correspond to the carpal bones, metacarpal bone, and phalanges of hand, in that order (Fig. 1-27).
Fig. 1-48. Talus, adjacent structures.
The talus meets the tibia and fibula to form the ankle joint. The talus covered by the medial and lateral malleoli (Fig. 1-43) is hardly touched on our body.
Fig. 1-49. Palpable bones of foot.
Instead, the calcaneus is easily touchable on the heel. A medial part of calcaneus to support the talus (sustentaculum tali) can be felt under the medial malleolus. On the medial side, the navicular and the 1st metatarsal bone can be felt; on the lateral side, the calcaneus, and the 5th metatarsal bone can be felt (Fig. 1-47).
The three cuneiforms (medial, intermediate, lateral cuneiforms) are located between the navicular and the 1st, 2nd, and 3rd metatarsal bones; they are also medial to the cuboid (Fig. 1-47). The metatarsal bones are not remarkable in the surface anatomy (Fig. 1-49).
In the foot, the many bones and their synovial joints (Fig. 2-32) relieve the impact.
The foot bones configurate the longitudinal and transverse arches of foot.
The longitudinal and transverse arches remind us of the Roman arches.
The individual bones encounter complex internal and external structures (e.g., muscles, ligaments, blood vessels, nerves), which result in numerous bone structures.