10 



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 organi- 

 sation, it becomes divided into distinct pieces, which constitute 

 vertebrae. 



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 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 : 



C 7 Cervical, 



True vertebrae 24 <J 12 Dorsal, 

 [ 5 Lumbar. 



False vertebrae 9 * 



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

 laminae, a spinous process, two transverse processes, and four articular 

 processes. The body is the solid part of the vertebra ; and, by its arti- 

 culation with adjoining vertebrae, gives strength and support 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 single irregular 

 opening, or several, for the exit of the venae basis vertebrae. 



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 protection of the 

 spinal cord. The upper and lower borders of the laminae are rough 

 for the attachment of the ligamenta subflava. The concavities 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 laminae of the vertebra ; they are intended for the 



