498 



DISSECTION OF THE THORAX. 



state of 

 ligaments. 



Bending to 

 side : 

 extent ; 



movement 

 of bones ; 



state of 

 ligaments. 



Rotation : 



movement 

 of bones ; 



where 

 present. 



each glide downwards on the upper ones of the next succeeding 

 bone. 



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

 Thus, the intervertebral discs are compressed behind, and stretched 

 in front ; the spinous and subflaval ligaments are relaxed ; the 

 anterior common ligament 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 last movement, this bend is least in the more 

 fixed upper dorsal vertebrae, and is greatest in the neck. 



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

 brought nearer together ; and they 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 inter- 

 vertebral substance compressed j 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 

 vertical axis through their centres, the fore part being turned to 

 the right or left, while the lower articular processes glide in the 

 opposite direction over the upper ones of the next bone below. The 

 movement will obviously be checked by the tightening of one set 

 of oblique fibres in the intervertebral disc. 



A pure rotation of this kind, however, takes place only to a 

 small extent in the upper dorsal region ; but in the neck a greater 

 degree of turning movement is permitted in combination with 

 lateral flexion, owing to the conformation of the articular surfaces. 

 In the loins the articular surfaces are so disposed that rotation is 

 impossible. 



