

ARTICULATIONS OF THE VERTEBRAL COLUMN 291 



on either side of the neck. In man it is merely the rudiment of an important elastic 

 ligament, which, in some of the lower animals, serves to sustain the weight of the 

 head. 



The Interspinal Ligaments (ligamenta inter spinalia; interspinous ligaments} 

 (Fig. 301). The interspinal ligaments thin and membranous, connect adjoining 

 spinous processes and extend from the root to the apex of each process. They 

 meet the ligamenta flava in front and the supraspinal ligament behind. They 

 are narrow and elongated in the thoracic region; broader, thicker, and quadrilateral 

 in form in the lumbar region; and only slightly developed in the neck. 



The Intertransverse Ligaments (ligamenta intertransversaria) . The intertransverse 

 ligaments are interposed between the transverse processes. In the cervical region 

 they consist of a few irregular, scattered fibers; in the thoracic region they are 

 rounded cords intimately connected with the deep muscles of the back; in the 

 lumbar region they are thin and membranous. 



Movements. The movements permitted in the vertebral column are: flexion, extension, 

 lateral movement, circumduction, and rotation. 



In flexion, or movement forward, the anterior longitudinal ligament is relaxed, and the inter- 

 vertebral fibrocartilages are compressed in front; while the posterior longitudinal ligament, the 

 ligamenta flava, and the inter- and supraspinal ligaments are stretched, as well as the posterior 

 fibers of the intervertebral fibrocartilages. The interspaces between the laminae are widened, 

 and the inferior articular processes glide upward, upon the superior articular processes of the 

 subjacent vertebrae. Flexion is the most extensive of all the movements of the vertebral column, 

 and is freest in the lumbar region. 



In extension, or movement backward, an exactly opposite disposition of the parts takes place. 

 This movement is limited by the anterior longitudinal ligament, and by the approximation of 

 the spinous processes. It is freest in the cervical region. 



In lateral movement, the sides of the intervertebral fibrocartilages are compressed, the extent 

 of motion being limited by the resistance offered by the surrounding ligaments. This movement 

 may take place in any part of the column, but is freest in the cervical and lumbar regions. 



Circumduction is very limited, and is merely a succession of the preceding movements. 



Rotation is produced by the twisting of the intervertebral fibrocartilages; this, although only 

 slight between any two vertebrae, allows of a considerable extent of movement when it takes place 

 in the whole length of the column, the front of the upper part of the column being turned to one 

 or other side. This movement occurs to a slight extent in the cervical region, is freer in the upper 

 part of the thoracic region, and absent in the lumbar region. 



The extent and variety of the movements are influenced by the shape and direction of the 

 articular surfaces. In the cervical region the upward inclination of the superior articular surfaces 

 allows of free flexion and extension. Extension can be carried farther than flexion; at the upper 

 end of the region it is checked by the locking of the posterior edges of the superior atlantal facets 

 in the condyloid fossae of the occipital bone; at the lower end it is limited by a mechanism whereby 

 the inferior articular processes of the seventh cervical vertebra slip into grooves behind and 

 below the superior articular processes of the first thoracic. Flexion is arrested just beyond the 

 point where the cervical convexity is straightened; the movement is checked by the apposition 

 of the projecting lower lips of the bodies of the vertebrae with the shelving surfaces on the bodies 

 of the subjacent vertebrae. Lateral flexion and rotation are free in the cervical region; they are, 

 however, always combined. The upward and medial inclinations of the superior articular surfaces 

 impart a rotatory movement during lateral flexion, while pure rotation is prevented by the slight 

 medial slope of these surfaces. 



In the thoracic region, notably in its upper part, all the movements are limited in order to 

 reduce interference with respiration to a minimum. The almost complete absence of an upward 

 inclination of the superior articular surfaces prohibits any marked flexion, while extension is 

 checked by the contact of the inferior articular margins with the laminae, and the contact of the 

 spinous processes with one another. The mechanism between the seventh cervical and the first 

 thoracic vertebrae, which limits extension of the cervical region, will also serve to limit flexion of 

 the thoracic region when the neck is extended. Rotation is free in the thoracic region: the 

 superior articular processes are segments of a cylinder whose axis is in the mid-ventral line of the 

 vertebral bodies. The direction of the articular facets would allow of free lateral flexion, but 

 this movement is considerably limited in the upper part of the region by the resistance of the 

 ribs and sternum. 



In the lumbar region flexion and extension are free. Flexion can be carried farther than exten- 

 sion, and is possible to just beyond the straightening of the lumbar curve; it is, therefore, greatest 

 at the lowest part where the curve is sharpest. The inferior articular facets are not in close appo- 



