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Henry Gray (1825–1861).  Anatomy of the Human Body.  1918.
 
 
3. The Vertebral Column
 
  
(Columna Vertebralis; Spinal Column).


The vertebral column is a flexuous and flexible column, formed of a series of bones called vertebræ.
  The vertebræ 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 vertebræ is, however, very rarely increased or diminished.
  The vertebræ in the upper three regions of the column remain distinct throughout life, and are known as true or movable vertebræ; those of the sacral and coccygeal regions, on the other hand, are termed false or fixed vertebræ, 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 vertebræ present certain common characteristics which are best studied by examining one from the middle of the thoracic region.
 
3a. 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 laminæ, and supports seven processes—viz., four articular, two transverse, and one spinous.


FIG. 82– A typical thoracic vertebra, viewed from above. (See enlarged image)

  When the vertebræ 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 vertebræ are two apertures, the intervertebral foramina, one on either side, for the transmission of the spinal nerves and vessels.

Body (corpus vertebræ).—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

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