The Ligaments connecting the Spinous Processes

These include supraspinous ligament, interspinous ligaments, and the liga- mentum nuchae.

The supraspinous ligament extends without interruption as a well-marked band of longitudinal fibers along the tips of the spines of the vertebrae from that of the seventh cervical downward till it ends on the median sacral crest.

Its more superficial fibers are much longer than the deep. The deeper fibers pass over adjacent spines only, while the superficial overlie several. It is connected laterally with the aponeurotic structures of the back; indeed, in the lumbar region, where it is well marked, it appears to result from the interweaving of the tendinous fibers 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 nuchae, or the posterior cervical ligament, 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 fibers 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 ligament, 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 are thin membranous structures which extend between the spines, and are connected with the ligamenta flava in front, and the supraspinous ligament behind.

The fibers pass obliquely from the root of one spine to the tip of the next; they thus decussate. They are best marked in the lumbar region, and are replaced by the well-developed interspinales muscles in the cervical region.