322 THE ARTICULATIONS 



together the apices of the spinous processes from the seventh cervical to the spinous 

 processes of the sacrum. It is thicker and broader in the lumbar than in the dorsal 

 region, and intimately blended, in both situations, with the neighboring aponeu- 

 rosis. The most superficial fibres of this ligament connect three or four vertebrae ; 

 those deeper-seated pass between two or three vertebrae ; whilst the deepest connect 

 the contiguous extremities of neighboring vertebrae. It is continued upward to 

 the external occipital protuberance, as the posterior margin of the ligamentum 

 nuchaa, which, in the human subject, is comparatively thin and forms an inter- 

 muscular septum. 



The Interspinous Ligaments (Fig. 227), thin and membranous, are interposed 

 between the spinous processes. Each ligament extends from the root to the 

 summit of each spinous process and connects together their adjacent margins. 

 They are narrow and elongated in the dorsal region ; broader, quadrilateral in 

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



5. LIGAMENTS CONNECTING THE TRANSVERSE PROCESSES. 

 Intertransverse. 



The Intertransverse Ligaments consist of bundles of fibres interposed 

 between the transverse processes. In the cervical region they consist of a few 

 irregular, scattered fibres ; in the dorsal, they are rounded cords intimately con- 

 nected with the deep muscles of the back ; in the lumbar region they are thin and 

 membranous. 



Actions. The movements permitted in the spinal column are, Flexion, Exten- 

 sion, Lateral Movement, Circumduction, and Rotation. 



In Flexion, or movement of the spine forward, the anterior common ligament 

 is relaxed, and the intervertebral substances are compressed in front, while the 

 posterior common ligament, the ligamenta subflava, and the inter- and supra- 

 spinous ligaments are stretched, as well as the posterior fibres of the intervertebral 

 disks. The interspaces between the laminae are widened, and the inferior articular 

 processes of the vertebrae above glide upward upon the articular processes of the 

 vertebrae below. Flexion is the most extensive of all the movements of the spine. 



In Extension, or movement of the spine backward, an exactly opposite dis- 

 position of the parts takes place. This movement is not extensive, being limited by 

 the anterior common ligament and by the approximation of the spinous processes. 



Flexion and extension are most free in the lower part of the lumbar region 

 between the third and fourth and fourth and fifth lumbar vertebrae ; above the 

 third they are much diminished, and reach their minimum in the middle and 

 upper part of the back. They increase again in the neck, the capability of motion 

 backward from the upright position being in this region greater than that of the 

 motion forward, whereas in the lumbar region the reverse is the case. 



In Lateral Movement, the sides of the intervertebral disks are compressed, the 

 extent of motion being limited by the resistance offered by the surrounding liga- 

 ments and by the approximation of the transverse processes. This movement may 

 take place in any part of the spine, but is most free in the neck and loins. 



Circum.duction is very limited, and is produced merely by a succession of the 

 preceding movements. 



Rotation is produced by the twisting of the intervertebral substances ; this, 

 although only slight between any two vertebrae, produces a great extent of move- 

 ment when it takes place in the whole length of the spine, the front of the 

 column being turned to one or the other side. This movement takes place only to 

 a slight extent in the neck, but is freer in the upper part of the dorsal region, and 

 is altogether absent in the lumbar region. 



It is thus seen that the cervical region enjoys the greatest extent of each 

 variety of movement, flexion and extension especially being very free. In the 

 dorsal region the three movements of flexion, extension, and circumduction are 

 only permitted to a slight extent, while rotation is very free in the upper part and 



