VERTEBRAL LIGAMENTS 231 



appears to result from the interweaving of the tendinous fibres of the several muscles which are 

 attached to the tips of the spinous processes. In the dorsal region it is a round slender cord 

 which is put on the stretch in flexion and relaxed in extension of the back. 



The ligamentum nuchas, or the posterior cervical hgament (fig. 269), is the 

 continuation in the neck of the supraspinous ligament, from which, however, it 

 differs considerably. It is a slender vertical septum of an elongated triangular 

 form, extending from the seventh cervical vertebra to the external protuberance 

 and the crest of the occipital bone. Its anterior border is firmly attached to the 

 tips of the spines of all the cervical vertebrae, including the posterior tubercle of 

 the atlas, as well as to the occiput. Its posterior border gives origin to the 

 trapezii, with the tendinous fibres of which muscle it blends. Its lateral, tri- 

 angular surfaces afford numerous points of attachment for the posterior muscles 

 of the head and neck. 



In man it is rudimentary, and consists of elastic and white fibrous tissues. As seen in the 

 horse, elephant, ox, and other pronograde mammals, it is a great and important elastic Ugament, 

 which even reaches along the thoracic part of the spinal column. In these animals it serves 



to support the head and neck, which otherwise from their own weight would hang down. Its 

 rudimentary state in man is the direct consequence of his erect position. 



The interspinous ligaments (fig. 270) are thin membranous structures which 

 extend between the spines, and are connected with the ligamenta flava in front^ 

 and the supraspinous ligament behind. -^ .' ,<— «' » ^'-^ 



The fibres pass obliquely from the root of one spine to the tip of the next; they thus decus- 

 sate. They are best marked in the lumbar region, and are replaced by the well-developed 

 interspinales muscles in the cervical region. 



(e) The Ligaments connecting the Transverse Processes 

 The intertransverse ligaments are but poorly developed. 



In the thoracic region they form small rounded bundles, and in the lumbar they are flat 

 membranous bands, unimportant as bonds of union. They consist of fibres passing between 

 the apices of the transverse processes. In the cervical region they are replaced by the inter- 

 transversarii muscles. 



The arterial supply for the column comes from twigs of the vertebral, ascending pharyn- 

 geal, ascending cervical, superior and aortic intercostals, lumbar, iUo-lumbar, and lateral sacral. 



The nerve-supply comes from the spinal nerves of each region. 



Movements. — The vertebral column is so formed of a number of bones and intervertebral 

 discs as to serve many purposes. It is the axis of the skeleton; upon it the skuU is supported; 

 and with it the cavities of the trunk and the Umbs are connected. As a fixed column it is capable 

 of bearing great weight, and, through the elastic intervertebral substances, of resisting and 

 breaking the transmission of shocks. Moreover, it is flexible. Now, the range of movements 

 of the column as a whole is very considerable; but the movements between any two vertebrae 

 are slight, so that motions of the spine may take place without any change in the shape of the 

 column, and without any marked disturbance in the relative positions of the vertebrae. It is ' 

 about the pulpy part of the intervertebral discs, which form a central elastic pivot or ball, upon 

 which the middle of the vertebrae rest, that these movements take place. 



The amount of motion is everywhere limited by the common vertebral Ugaments, but it 

 depends partly upon the width of the bodies of the vertebrae, and partly upon the depth of the 

 discs, so that in the loins, where the bodies are large and wide, and the discs very thick, free 

 motion is permitted; in the cervical region, though the discs are thinner, yet, as the bodies are 

 smaller, almost equally free motion is allowed. As the ball-hke pulpy part of the intervertebral \ 

 disc is the centre of movement of each vertebra, it is obvious that the motion would be of _a 1 

 roUing character in any direction but for the articular processes, wnich serve also to give steadi- / 

 ness to the column and to assist in bearing the superincumbent weight. Were it not for these 

 processes, the column, instead of being steady, endowed with the capacity of movement by 

 muscular agency, would be tottering, requiring muscles to steady it. The influence of the 

 articular processes in limiting the direction of incUnation will appear from a study of the 

 movements in the three regions of the spine. 



In the neck all movements are permitted and are free, except between the second and third ^ 

 cer\ncal vertebrae, where they are slight, owing to the shallow intervertebral disc and the great -^ 

 prolongation of the anterior hp of the inferior surface of the body of the epistropheus, which 

 checks forward flexion considerably. On the whole, however, extension and lateral inclination 

 are more free and extensive in this than in any other region of the column, whilst flexion is more 

 limited than in the lumbar region. Rotatory movements are also free, but take place, on ac- 

 count of the position and incUnation of the articular facets, not, as in the thoracic region, round 

 a vertical axis, but round an oblique axis, the articular process of one side gliding upward and 

 forward and that of the opposite side downward and backward. 



In the thoracic region, especially near its middle, antero-posterior flexion and extension 

 are very slight; and, as the concavity of the curve here is forward, the flat and nearly vertical 

 surfaces of the articular processes prevent anything like sliding in a curvilinear manner of the 



