LIGAMENTS OF VERTEBRA. 349 



The surfaces of the vertebrae in contact with the disk have a cartilagin- 

 ous covering; this may be seen by cutting the intervertebral substance 

 from the bone. Over the centre of the 



osseous surface it forms a continuous layer, Fig. 1]3. 



but towards the circumference it consists of 

 separate pieces. 



The disks are thicker between the lum- 

 bar and cervical, than between the upper 

 and middle dorsal vertebras; and where the 

 spinal column is arched forwards, as in the 

 loins and neck, they are deepest at the an- 

 terior edge, being wedge-shaped. The thin- 

 nest piece is situate between the second and 

 third cervical vertebrae, and the thickest 

 between the fifth lumbar and the sacrum. 



Use. The intervertebral substance unites 

 together the vertebrae so firmly as to pre- A HORTZOSFAL CUT THROUGH AN in- 

 vent displacement of those bones without WRVKRTHB.UL FIBKO-CARILAH. 



rupture of it. " Laminarexternal P art - 



P ' . i , ,. i 6. Pulpy central part of the fibro-carti- 



By means of the central elastic part the la ^j 

 revolving motion of one bone on another is 



produced ; and the degree of the movement is limited by the circumferen- 

 tial laminar portion. 



Through its wedge-shaped form the disk is chiefly instrumental in giving 

 rise to the convexity of the spinal column in the loins and neck ; and 

 through its elasticity it moderates the effect of jars or shocks transmitted 

 from bone to bone. 



The depth of its several pieces amounts to about a fourth of the length 

 of the movable part of the spinal column ; but as it yields under pressure, 

 the height of the body will be shorter from half an inch to an inch in the 

 course of the day, according to the fatigue undergone. 



LIGAMENTS OF THE NEURAL ARCH AND PROCESSES. The several pro- 

 cesses of the vertebrae have special uniting ligaments: thus the articular 

 processes are joined by a capsule and a synovial membrane ; the neural 

 arches are connected by yellow ligaments ; the spinous processes have one 

 band along the tip and another between them ; arid the transverse pro- 

 cesses are provided with intervening bands of fibres. 



Ligaments of Articulating processes. Between the articulating processes 

 there is a movable joint, in which the bones are covered with cartilage, 

 and are surrounded by a loose capsnlar ligament of scattered fibres, en- 

 closiug a synovial membrane. In the cervical part of the spine the cap- 

 sular ligaments are looser than in the dorsal or lumbar region. 



Movement. With flattened articular surfaces is combined a gliding of 

 one bone upon another. This movement is least limited in the neck, the 

 loins, and the lower dorsal vertebrre. 



By the difference in the shape of the articulating processes, the kind of 

 motion in the spine is determined; and by their arrangement the degree 

 is limited, and the vertebrae are partly maintained in situ. In dislocation 

 of the spinal column they are generally broken before a vertebra can be 

 dislodged from its imbricated position. 



Ligaments of the arches. The ligamenta sub/lava (fig. 114, 2 ) so named 

 from their color, are situate between the neural arches of the vertebra 1 , 

 and close the spinal canal behind. Between each pair of arjhes are two 



