ARTICULATIONS OF THE VERTEBRA. 125 



below it ; those more deeply seated reach only from one to the next, or the 

 second below it. 



The ligamentum nuchce is the continuation upwards of the supraspinous 

 ligament. It is, in the human subject, a thin intermuscular septum of 

 elastic and white fibrous tissue, the most superficial 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 derives importance as 

 the representative of a strong elastic structure in other animals. 



The intertransverse ligaments are unimportant bands extending between 

 the transverse processes. In the lumbar region they are membranous, in the 

 dorsal region they are rounded bundles intimately connected with the 

 muscles of the back ; and in the neck they are usually reduced to a few- 

 irregular fibres, which may in some instances be wanting. 



MOVEMENTS. The movement of flexion and extension of the vertebral column is 

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

 small amount of intervertebral substance and the imbrication of the laminae. The 

 greatest bending backwards is permitted in the cervical, the greatest bending 

 forwards in the lumbar region, especially between the fourth and fifth lumbar 

 vertebrae. Movements in other directions are limited chiefly by the articulating 

 processes. In the dorsal region the articulating surfaces of each vertebra lie in the arc 

 of a circle whose centre is in front of the vertebra, and round tnis centre a consider- 

 able degree of rotation is permitted. In the lumbar region, the centre of the circle 

 in which the articular surfaces lie being placed behind, rotation would involve an 

 amount of motion between the bodies of the vertebrae that is impossible ; the articu- 

 lating processes, however, fit sufficiently loosely to permit of lateral flexion, and by 

 combination of this with antero-posterior flexion, some degree of circumduction is 

 produced. The articulating surfaces of the cervical vertebrae, being oblique and 

 placed in nearly the same transverse plane, allow neither pure rotation nor pure 

 lateral flexion. They permit, besides forward and backward motion, only one other, 

 which is rotatory round an oblique axis the inferior articulating process of one side 

 gliding upwards and forwards on the opposing surface, and that of the other side 

 gliding downwards and backwards, by which a combination of lateral flexion and 

 rotation is obtained. The reader who may wish to pursue more minutely the study 

 of the movements of the joints may consult the work of W. and E. Weber already 

 cited ; H. Meyer, "Handbuck der Physiol. Auat. ;"and Henke, "Handbuch der Anat. 

 und Mech. der Gelenke/' 1864. 



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 articular surfaces 

 of the axis and with the condyles of the occipital bone. The capsule of the 

 atlanto-axial joint is strengthened behind by an accessory ligament, directed 

 downwards and inwards to the body of the axis near the base of the 

 odontoid process. 



The transverse ligament of the atlas is a strong and thick band, which 

 extends across the ring of the atlas, and retains the odontoid process in its 

 place. It is attached on each side to the impression below the inner border 

 of the superior articulating process. It is arched backwards behind the 

 odontoid process, and is broadened out in the middle line. From the 

 middle of its posterior surface a short thin bundle of fibres passes down to 

 be attached to tho body of the axis, whilst another passes up to the basilar 



