VERTEBRAL LIGAMENTS. 137 



atlas, nor between the latter and the axis ; common fibrous membrane 

 supplies their place in these two spaces, constituting posterior occipito- 

 atlantal and atlauto-axial ligaments. 



The interspinous ligaments, thin and rather membranous, have an 

 attachment extending from the root to near the summit of each spinous 

 process, and connect the inferior border of one with the superior border ^• 

 of that next below it. They are best seen in the lumbar region, and are 

 least developed in the neck. 



The supraspinous ligaments consist of small compressed bundles 

 of longitudinal fibres, which connect the summits of the spinous pro- 

 cesses, and form a continuous chain from the seventh cervical vertebra 

 to the spine of the sacrum. The superficial fibres pass down from a 

 given vertebra to the third or fourth below it ; those more deeply 

 seated reach only from one to the next, or the second below it. 



The ligamentum nuchas is the continuation upwards of the 

 supraspinous ligament. It is, in the human subject, a thin inter- 

 muscular septum of elastic and white fibrous tissue, the most super- 

 ficial part of which extends from the spine of the seventh cervical 

 vertebra to the occipital protuberance, while the deeper fibres, springing 

 from the same origin, pass to the occipital spine, and the spines of the 

 six upper vertebrae. It is the representative of a strong elastic struc- 

 ture which suspends the head in the lower animals. 



The intertransverse ligaments are unimportant bands extending 

 between the transverse processes. In the lumbar regions they are 

 membranous, in the dorsal region they are rounded bundles intimately 

 connected with the muscles of the back ; and in the neck they arc 

 usually reduced to a few irregular fibres, which may in some instances 

 be wanting. 



Movements.— The movements of flexion and extension of the vertebral column 

 are freely allowed in the cervical and lumbar regions, but in the dorsal are limited 

 by the small amount of intervertebral substance and the imbrication of the 

 laminas. The greatest bending backwards is permitted in the cervical, the 

 greatest bending forwards in the lumbar region, especially between the fourth 

 and fifth lumbar vertebras. Movements in other directions are limited chieflj' by 

 the articular processes. In the dorsal region the articular surfaces of each verte- 

 bra lie in the arc of a circle whose centre is in front of the vertebras, and round 

 this centre a considerable degree of rotation is pennitted. In the lumbar 

 region, the centre of the circle in which the ai-ticular surfaces lie is placed behind, 

 so that rotation is i^revented : the articular iirocesses, however, fit sufficientlj^ 

 loosely to iieimit of lateral flexion, and by combination of this with antero-po.?.- 

 terior flexion, some degree of circumdiiction is produced. The articular sur- 

 faces of the cervical vertebrae, being oblique and placed in nearly the same trans- 

 verse plane, allow neither pure rotation nor jiure lateral flexion. They pennit, 

 besides foiTv^ard and backward motion, only one other, which is rotatorj^ round 

 an oblique axis — the inferior articulatmg process of one side gliding upwards 

 and forwards on the ojiposmg surface, and that of the other side gliding down- 

 wards and backfl-ards, by which a combmation of lateral flexion and rotation is 

 obtained. 



ARTICULATIONS OF THE ATLAS, AXIS, AND OCCIPITAL BONE. 



The atlas, axis, and occipital bone are connected by articular surfaces 

 and ligaments, without the presence of intervertebral discs. 



Two pairs of synovial articulations, surrounded by capsular 

 ligaments, connect the lateral masses of the atlas with the superior 



