OF THE MOTOBY APPAEATUS IN MAN. 



139 



7 cervical (c) ; 12 dorsal (d) ; 5 lumbar (I)-, 5 sacral (s); and 

 4 coccygeal (or). It presents several curves when viewed in 

 profile, but is straight when seen from before 

 backwards, or from behind forwards. At first 

 all the vertebrae are distinct, but with years 

 certain of them become fused into one or more : 

 the 5 sacral vertebras generally unite so as to 

 form one mass ; and the coccygeal bones are also 

 disposed to fuse into one bone in the adult. 



The essential character of a vertebra (with 

 certain exceptions, however) is to be formed or 

 composed of a body and processes, and to have 

 a foramen, or short canal, behind the body, in 

 which the spinal marrow and its membranes are 

 lodged. But the coccygeal vertebrae in man are 

 quite rudimentary, and cannot be included in 

 this definition. At the sides of the column are 

 openings for the passage of the nerves ; they are 

 called the foramina intervertebralia, and are 

 generally formed by the union of two vertebrae. 



The body or centrum of a vertebra is a disc K ff' 92 - 

 (a), with parallel surfaces, each united (with cer- 

 tain exceptions) to the adjoining vertebra by a substance 

 called inter vertebral ; this is a fibro-cartilage of great strength, 

 flexibility, and elasticity, on which the strength 

 and mobility of the column greatl} r depends. 



Four articular processes also greatly contri- 

 bute to its strength, and limit its movements in 

 certain directions. The spinous process (neural 

 spine) 6, as well as the transverse processes or 

 parapophyses c, give attachments to numerous 

 muscles, and the latter support the ribs. 



The mobility of the column varies in different 

 regions, being most extensive in the neck and loins. The 

 erector muscles of the spine, those intended merely to raise 

 the body upright, and to counterbalance the weight of all the 

 viscera situated in front, are placed on the dorsal side of the 

 column, filling up the grooves called vertebral, and which may 

 be seen extending on either side the spinous processes, from 

 the head quite to the extremity of the sacral vertebras. They 

 seek attachments also in the ribs and transverse processes of 

 the vertebrae. 



The spinous processes (neural spines) are long and powerful 



Fig. 93. 



