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OSTEOLOGY 



THE VERTEBRAL COLUMN (COLUMNA VERTEBRALIS ; SPINAL 



COLUMN). 



The vertebral column is a flexuous and flexible column, formed of a series of 

 bones called vertebrae. 



The vertebrae are thirty- three in number, and are grouped under the names 

 cervical, thoracic, lumbar, sacral, and coccygeal, according to the regions they 

 occupy; there are seven in the cervical region, twelve in the thoracic, five in the 

 lumbar, five in the sacral, and four in the coccygeal. 



This number is sometimes increased by an additional vertebra in one region, 

 or it may be diminished in one region, the deficiency often being supplied by an 

 additional vertebra in another. The number of cervical vertebras is, however, 

 very rarely increased or diminished. 



The vertebras in the upper three regions of the column remain distinct through- 

 out life, and are known as true or movable vertebras; those of the sacral and 

 coccygeal regions, on the other hand, are termed false or fixed vertebrae, because 

 they are united with one. another in the adult to form two bones five forming 

 the upper bone or sacrum, and four the terminal bone or coccyx. 



With the exception of the first and second cervical, the true or movable vertebras 

 present certain common characteristics which are best studied by examining one 

 from the middle of the thoracic region. 



GENERAL CHARACTERISTICS OF A VERTEBRA. 



A typical vertebra consists of two essential parts viz., an anterior segment, the 

 body, and a posterior part, the vertebral or neural arch; these enclose a foramen, 

 the vertebral foramen. The vertebral arch consists of a pair of pedicles and a pair 

 of laminae, and supports seven processes viz., four articular, two transverse, and 

 one spinous. 



Costal fovea 



Pedicle or roof of 

 vertebral arch 



Lamina 



Superior articular process 



FIG. 82. A typical thoracic vertebra, viewed from above. 



When the vertebras are articulated with each other the bodies form a strong 

 pillar for the support of the head and trunk, and the vertebral foramina constitute 

 a canal for the protection of the medulla spinalis (spinal cord), while between 

 every pair of vertebrae are two apertures, the intervertebral foramina, one on 

 either side, for the transmission of the spinal nerves and vessels. 



Body (corpus vertebra). The body is the largest part of a vertebra, and is 

 more or less cylindrical in shape. Its upper and lower surfaces are flattened and 



