MOTION OF SPINAL COLUMN. 351 



ligaments are thin membranous bands in the intervals between the pro- 

 cesses. In the dorsal vertebrae they are round bundles of fibres (fig. 115, *). 

 And in the neck the fibres exist only at the apex of the processes, or they 

 may be wanting here and there. 



LIGAMENTS OF SPECIAL VERTEBRA. The ligaments of the first two 

 cervical, and the sacral and coccygeal vertebrae, will be given with the 

 dissection of the neck (pp. 166, 167) and of the pelvis (Section vii.). 



MOVEMENTS OF SPINAL COLUMN. The spinal column can be bent for- 

 wards, backwards, and to each side ; and can be rotated. 



Inflexion the vertebrae between the axis and sacrum are bowed for- 

 wards. The greatest movement takes place between the last two lumbar 

 vertebrae and the sacrum (Humphry) ; there is an intermediate degree 

 in the neck ; and the least is in the upper half of the dorsal region, where 

 the ribs are united to the sternum. 



The bodies of the bones are brought nearer together in front, whilst 

 they are separated behind. The inferior pair of articular processes of the 

 second vertebra glide upwards on the upper articular of the third vertebra ; 

 the inferior of the third bone move in like manner on the upper processes 

 of the fourth ; and so on throughout the movable column. 



The ligament in front of the bodies is loose, but the posterior, and those 

 uniting the neural arches and processes, are stretched. The fore part of 

 each inter vertebral disk is squeezed and thinner, and the back is elongated. 



In extension, the vertebrae are arched backwards, but not to so great a 

 degree as when the spine is bent forwards. The motion is most in the 

 neck ; and is least in the dorsal vertebrae, which are fixed by the true ribs 

 and the sternum, and are impeded in their movement by the overlapping 

 spinous processes. 



The posterior parts of the vertebrae are approximated, whilst the ante- 

 rior are separated ; and the inferior articular processes of each (from the 

 second cervical to the sacrum) glide downwards, on the upper articular 

 processes of the next succeeding bone. 



The condition of the ligaments is the opposite to that in flexion. Thus, 

 the intervertebral disks are compressed behind and widened before ; the 

 spinous and subflaval are relaxed ; the anterior common of the bodies is 

 tightened, and the hinder band is slackened. 



Lateral inclination. The spine can be curved to the right or the left 

 side. Like the other movements, this is least in the more fixed upper 

 dorsal vertebras, and is greatest in the neck. 



On the concave side of the curve, say the right, the bodies are brought 

 nearer together ; and are carried away from each other on the opposite 

 aspect. The right inferior articular surface glides down, and the left up, 

 in the joints with the vertebra beneath. 



On the right side the ligaments will be relaxed and the intervertebral 

 substance compressed ; and on the left those structures will be tightened 

 so as to check the movement. 



Rotation is the twisting of the bodies of the vertebrae around a line 

 through their centres, the fore part being turned to the right and to the 

 left. Its degree is greatest in the cervical and the upper dorsal vertebras, 

 but is absent in the lumbar part of the column. 



The vertebral bodies are directed horizontally, and the articular pro- 

 cesses move differently on the two sides. Supposing the face turned to 

 the right, the processes of the right side glide inwards towards, and those 

 of the left side outwards from the spinal canal. 



