Self-taught class 2. The bones of the shoulder girdle: the scapula and clavicle. The ribs, the sternum. Thorax as a whole

Self-taught class 3. Bones of the foot. X-rays anatomy of the bones.
The aim: to learn topography and structure of the bones composing the skeleton of the foot; to name and show on the samples the anatomical structures of these bones; to learn how to identify the structure of bones on X-ray films.

Professional orientation: knowledge of this topic is necessary for doctors of all the specialities, especially for neuropathologists, neurosurgeons, traumatologists, orthopedists, pediatritians and others.

The plan of the self-taught class:

1. 
   Put the skeleton of the foot to the right position and learn what three parts it consists of.
   
2. 
   Learn the structures of the bones of each part of the foot and identify them on the samples.
   
3. 
   Learn how to identify general parts of bones (diaphysis, epiphyses, apophyses) on X-ray films.
   
4. 
   Learn how to identify the bones of the upper and lower extremities on the X-ray films.
   

The skeleton of the human being may be studied with X-rays method. Compact bony tissue makes a dense shadow on X-ray film, which is visible as light stripes of different width, and cancellous bony tissue performs a retiform picture with dark spots. Bony cavities filled with soft tissues (e.g. orbit) or air (e.g. nasal cavity, paranasal sinuses) are seen as large dark formations, bounded with light lines correspond to their bony walls. Sulci on the bone surface and sinuses of dura mater encephali perform dark lines on roentgenogram.

In the place of junction of bones a dark stripe is observed, the width of that stripe depending on the thickness of the articular cartilage.

Points of ossification, visible on X-ray photograph, may serve to define the age of the patient or trace the fusion of bone parts (appearance of synostosis).

Ossification of the Vertebral Column.–Each cartilaginous vertebra is ossified from three primary centers, two for the vertebral arch and one for the body. Ossification of the vertebral arches begins in the upper cervical vertebrae about the seventh or eighth week of fetal life, and gradually extends down the column. The ossific granules first appear in the situations where the transverse processes afterward project, and spread backward to the spinous process forward into the pedicles, and lateralward into the transverse and articular processes. Ossification of the bodies begins about the eighth week in the lower thoracic region, and subsequently extends upward and downward along the column. The center for the body does not give rise to the whole of the body of the adult vertebra, the postero-lateral portions of which are ossified by extensions from the vertebral arch centers. The body of the vertebra during the first few years of life shows, therefore, two synchondroses, neurocentral synchondroses, traversing it along the planes of junction of the three center. In the thoracic region, the facets for the heads of the ribs lie behind the neurocentral synchondroses and are ossified from the centers for the vertebral arch. At birth the vertebra consists of three pieces, the body and the halves of the vertebral arch. During the first year the halves of the arch unite behind, union taking place first in the lumbar region and then extending upward through the thoracic and cervical regions. About the third year the bodies of the upper cervical vertebrae are joined to the arches on either side; in the lower lumbar vertebrae the union is not completed until the sixth year. Before puberty, no other changes occur, excepting a gradual increase of these primary centers, the upper and under surfaces of the bodies and the ends of the transverse and spinous processes being cartilaginous. About the sixteenth year, five secondary centers appear, one for the tip of each transverse process, one for the extremity of the spinous process, one for the upper and one for the lower surface of the body. These fuse with the rest of the bone about the age of twenty-five.

Ossification of Ribs.–Each rib, with the exception of the last two, is ossified from four centers; a primary center for the body, and three epiphysial centers, one for the head and one each for the articular and non-articular parts of the tubercle. The eleventh and twelfth ribs have each only two centers, those for the tubercles being wanting. Ossification begins near the angle toward the end of the second month of fetal life, and is seen first in the sixth and seventh ribs. The epiphyses for the head and tubercle make their appearance between the sixteenth and twentieth years, and are united to the body about the twenty-fifth year.

Ossification of Sternum.–The sternum originally consists of two cartilaginous bars, situated one on either side of the median plane and connected with the cartilages of the upper nine ribs of its own side. These two bars fuse with each other along the middle line to form the cartilaginous sternum which is ossified from six centers: one for the manubrium, four for the body, and one for the xiphoid process. The ossific centers appear in the intervals between the articular depressions for the costal cartilages, in the following order: in the manubrium and first piece of the body, during the sixth month; in the second and third pieces of the body, during the seventh month of fetal life; in its fourth piece, during the first year after birth; and in the xiphoid process, between the fifth and eighteenth years. The centers make their appearance at the upper parts of the segments, and proceed gradually downward. To these may be added the occasional existence of two small episternal centers, which make their appearance one on either side of the jugular notch; they are probably vestiges of the episternal bone of the monotremata and lizards. Occasionally some of the segments are formed from more than one center, the number and position of which vary. Thus, the first piece may have two, three, or even six centers. When two are present, they are generally situated one above the other, the upper being the larger; the second piece has seldom more than one; the third, fourth, and fifth pieces are often formed from two centers placed laterally, the irregular union of which explains the rare occurrence of the sternal foramen, or of the vertical fissure which occasionally intersects this part of the bone constituting the malformation known as fissura sterni; these conditions are further explained by the manner in which the cartilaginous sternum is formed. More rarely still the upper end of the sternum may be divided by a fissure. Union of the various centers of the body begins about puberty, and proceeds from below upward; by the age of twenty-five they are all united. The xiphoid process may become joined to the body before the age of thirty, but this occurs more frequently after forty; on the other hand, it sometimes remains ununited in old age. In advanced life the manubrium is occasionally joined to the body by bone. When this takes place, however, the bony tissue is generally only superficial, the central portion of the intervening cartilage remaining unossified.

Ossification of Humerus.–The humerus is ossified from eight centers, one for each of the following parts: the body, the head, the greater tubercle, the lesser tubercle, the capitulum, the trochlea, and one for each epicondyle. The center for the body appears near the middle of the bone in the eighth week of fetal life, and soon extends toward the extremities. At birth the humerus is ossified in nearly its whole length, only the extremities remaining cartilaginous. During the first year, sometimes before birth, ossification commences in the head of the bone, and during the third year the center for the greater tubercle, and during the fifth that for the lesser tubercle, make their appearance. By the sixth year the centers for the head and tubercles have joined, so as to form a single large epiphysis, which fuses with the body about the twentieth year. The lower end of the humerus is ossified as follows. At the end of the second year ossification begins in the capitulum, and extends medialward, to form the chief part of the articular end of the bone; the center for the medial part of the trochlea appears about the age of twelve. Ossification begins in the medial epicondyle about the fifth year, and in the lateral about the thirteenth or fourteenth year. About the sixteenth or seventeenth year, the lateral epicondyle and both portions of the articulating surface, having already joined, unite with the body, and at the eighteenth year the medial epicondyle becomes joined to it.

Ossification of Ulna–The ulna is ossified from three centers: one each for the body, the inferior extremity, and the top of the olecranon. Ossification begins near the middle of the body, about the eighth week of fetal life, and soon extends through the greater part of the bone. At birth the ends are cartilaginous. About the fourth year, a center appears in the middle of the head, and soon extends into the styloid process. About the tenth year, a center appears in the olecranon near its extremity, the chief part of this process being formed by an upward extension of the body. The upper epiphysis joins the body about the sixteenth, the lower about the twentieth year.

Ossification of Radius.–The radius is ossified from three centers: one for the body, and one for either extremity. That for the body makes its appearance near the center of the bone, during the eighth week of fetal life. About the end of the second year, ossification commences in the lower end; and at the fifth year, in the upper end. The upper epiphysis fuses with the body at the age of seventeen or eighteen years, the lower about the age of twenty. An additional center sometimes found in the radial tuberosity, appears about the fourteenth or fifteenth year.

Ossification of the Bones of the Hand.–The carpal bones are each ossified from a single center, and ossification proceeds in the following order in the capitate and hamate, during the first year, the former preceding the latter; in the triangular, during the third year; in the lunate and greater multangular, during the fifth year, the former preceding the latter; in the navicular, during the sixth year; in the lesser multangular, during the eighth year; and in the pisiform, about the twelfth year

Occasionally an additional bone, the os centrale, is found on the back of the carpus, lying between the navicular, lesser multangular, and capitate. During the second month of fetal life it is represented by a small cartilaginous nodule, which usually fuses with the cartilaginous navicular. Sometimes the styloid process of the third metacarpal is detached and forms an additional ossicle.

The metacarpal bones are each ossified from two centers: one for the body and one for the distal extremity of each of the second, third, fourth, and fifth bones; one for the body and one for the base of the first metacarpal bone. The first metacarpal bone is therefore ossified in the same manner as the phalanges, and this has led some anatomists to regard the thumb as being made up of three phalanges, and not of a metacarpal bone and two phalanges. Ossification commences in the middle of the body about the eighth or ninth week of fetal life, the centers for the second and third metacarpals being the first, and that for the first metacarpal, the last, to appear; about the third year the distal extremities of the metacarpals of the fingers, and the base of the metacarpal of the thumb, begin to ossify; they unite with the bodies about the twentieth year.

The phalanges are each ossified from two centers: one for the body, and one for the proximal extremity. Ossification begins in the body, about the eighth week of fetal life. Ossification of the proximal extremity commences in the bones of the first row between the third and fourth years, and a year later in those of the second and third rows. The two centers become united in each row between the eighteenth and twentieth years.

In the ungual phalanges the centers for the bodies appear at the distal extremities of the phalanges, instead of at the middle of the bodies, as in the other phalanges. Moreover, of all the bones of the hand, the ungual phalanges are the first to ossify.

Ossification of the Bones of the Foot–The tarsal bones are each ossified from a single center, excepting the calcaneus, which has an epiphysis for its posterior extremity. The centers make their appearance in the following order: calcaneus at the sixth month of fetal life; talus, about the seventh month; cuboid, at the ninth month; third cuneiform, during the first year; first cuneiform, in the third year; second cuneiform and navicular, in the fourth year. The epiphysis for the posterior extremity of the calcaneus appears at the tenth year, and unites with the rest of the bone soon after puberty. The posterior process of the talus is sometimes ossified from a separate center, and may remain distinct from the main mass of the bone, when it is named the os trigonum.

The metatarsal bones are each ossified from two centers: one for the body, and one for the head, of the second, third, fourth, and fifth metatarsals; one for the body, and one for the base, of the first metatarsal. Ossification commences in the center of the body about the ninth week, and extends toward either extremity. The center for the base of the first metatarsal appears about the third year; the centers for the heads of the other bones between the fifth and eighth years; they join the bodies between the eighteenth and twentieth years.

The phalanges are each ossified from two centers: one for the body, and one for the base. The center for the body appears about the tenth week, that for the base between the fourth and tenth years; it joins the body about the eighteenth year.
Practice skills
See practice class 6 – “Bones of the leg and food (tarsal, metatarsal, skeleton of fingers). X-ray-anatomy of bones.”

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