VERTEBRAL COLUMN. 23 



VERTEBRAL COLUMN. 



The Vertebral column is the first and only rudiment of internal 

 skeleton in the lower Vertebrata, and constitutes the type of that 

 great division of the animal kingdom. It is also the first developed 

 portion of the skeleton in man, and the centre around which all the 

 other parts are produced. In its earliest formation it is a simple 

 cartilaginous cylinder, surrounding and protecting the primitive 

 trace of the nervous system ; but, as it advances in growth and or- 

 ganization, it becomes divided into distinct pieces, which constitute 

 vertebra. 



The vertebrae are divided into true and false. The true vertebrae 

 are twenty-four in number, and are classified according to the three 

 regions of the trunk which they occupy, into the cervical, dorsal, and 

 lumbar. The false vertebrae consist of nine pieces united into two 

 bones, the sacrum and coccyx. The arrangement of the vertebrae 

 may be better comprehended by means of the accompanying table : 



( 7 Cervical, 



True vertebrae 24 12 Dorsal, 



( 5 Lumbar. 



False vertebrae 9 ( 5 Sacrum, 



( 4 Coccyx. 



Characters of a Vertebra. A vertebra consists of a body, two 

 laminae, a spinous process, two transverse processes, and four ar- 

 ticular processes. The body is the solid part of the vertebra ; and 

 by its articulation with adjoining vertebras, gives strength and sup- 

 port to the trunk. It is flattened above, and below, convex in front, 

 and slightly concave behind. Its anterior surface is constricted 

 around the middle, and pierced by a number of small openings 

 which give passage to nutritious vessels. Upon its posterior surface 

 is a singular irregular opening, or several, for the exit of the vena 

 basis vertebrcB or vertebral sinuses. 



The lamina commence upon the sides of the posterior part of the 

 body of the vertebra by two pedicles ; they then expand, and 

 arching backwards, enclose a foramen which serves for the protec- 

 tion of the spinal cord. The upper and lower borders of the laminae 

 are rough for the attachment of the ligamenta subflava. The con- 

 cavities above and below the pedicles are the intervertebral notches. 

 The spinous process stands backwards from the angle of union of 

 the laminae of the vertebra. It is the succession of these projecting 

 processes along the middle line of the back, that has given rise to 

 the common designation of the vertebral column the spine. The 

 use of the spinous process is for the attachment of muscles. The 

 transverse processes project one at each side from the laminas of the 

 vertebra ; they are intended for the attachment of muscles. The 

 articular processes, four in number, stand upwards and downwards 

 from the laminae of the vertebras to articulate with the vertebra 

 above and below. 



