LIGAMENTS OF THE VERTEBRAL COLUMN. 139 



interposed between each of the vertebrae from the axis to the sacrum, and 

 retaining them firmly in connexion with each other. It differs in thick 

 ness in different parts of the column, and varies in depth at different points 

 of its extent ; thus, it is thickest in the. lumbar region, deepest in front in 

 the cervical and lumbar regions, and behind in the dorsal region ; and 

 contributes, in a great measure, to the formation of the natural curves of 

 the vertebral column. 



When the intervertebral substance is bisected either horizontally or 

 vertically, it is seen to be composed of a series of layers of dense fibrous 

 tissue, separated by interstices filled with the softer kind. The central 

 part of each intervertebral disc is wholly made up of this softer fibrous 

 cartilage, which has the appearance of a pulp, and is so elastic as to rise 

 above the level of the section as soon as its division is completed. When 

 examined from the front, the layers are found to consist of fibres passing 

 obliquely between the two vertebrae, in one layer passing from left to 

 right, in the next from right to left, alternating in each successive layer. 



ARCHES. t The ligamenta subflava are two 

 thin planes, of yellow fibrous tissue, situated be- 

 tween the arches of each pair of vertebrae, from 

 the axis to the sacrum. From the imbricated 

 position of the laminae they are attached to the 

 posterior surface of the vertebra below, and to 

 the anterior surface of the arch of the vertebra 

 above, and are separated from each other at the 

 middle line by a slight interspace. They coun- 

 teract by their elasticity, the efforts of the flexor 

 muscles of the trunk ; and by preserving the 

 upright position of the spine, limit the expendi- 

 ture of muscular force. They are longer in the 



cervical than in the other regions of "the spine, and are thickest in the 

 lumbar region. 



The ligamenta subflava are in relation by both surfaces with the 

 meningo-rachidian veins, and internally they are separated from the dura 

 mater of the spinal cord by those ^ eins and some loose areolar and adipose 

 tissue. 



ARTICULAR PROCESSES. The ligaments of the articular processes of the 

 vertebrae are loose synovial capsules which surround the articulating sur- 

 faces. They are protected on their external side by a thin layer of liga- 

 mentous fibres. 



SPINOUS PROCESSES. The inter-spinous ligaments are thin and mem- 

 branous, and are extended between the spinous processes in the dorsal 

 and lumbar regions. They are thickest in the latter region ; and are in 

 relation with the multifidus spinae muscle at each side. 



The 8upra8pmou* ligament (fig. 82) is a strong and inelastic fibrous 

 cord, which extends from the apex of the spinous process of the last cer- 

 vical vertebra to the sacrum, being attachecl to each spinous process in its 

 course ; it is thickest in the lumbar region. The continuation of this liga- 

 ment upwards to the tuberosity of the occipital bone, constitutes the rudi- 

 mentary ligamentum nuchce of man. The latter is strengthened, as in 



* An internal view of the arches of three vertebra?. To obtain this view the lamina 

 have been divided through their pedicles. 1. One of the ligamenta subflava. 2 Tne 

 capsular ligament of one side. 



