ARTICULATIONS OF THE SPTNE. 188 



ligaments appear to be produced by the two fil)rous planes of the preceding 

 ligaments, which, on arriving at the base of the spinous processes, separate from 

 one another to be carried outwards. Their anterior border is inserted into the 

 posterior margin of the \'ertebral lamina in front, Their jwsterior border is fixed 

 to the anterior border and inferior face of the lamina behind. Their suj erior 

 face is in relation with some spinal muscles, and their inferior face is in contact 

 with the dura mater. Outwardly, they are confounded with the capsules proper 

 to the articular processes. Yellow and elastic in the cervical region, these 

 ligaments are white and inelastic in the dorso-lunibar region. 



Characters proper to some Intervertebral Articulations. 1. Infer- 

 eorri/geul and sacro-corri/ijpaJ artirulations. — These articulations are adapted to the 

 rudimentary type of the vertebrae they unite. The coccygeal bones only come iu 

 contact by their bodies — their spinal laminge being reduced to the merest traces, 

 or are altogether absent. The anterior and posterior articular surfaces of each 

 vertebra are convex, and the interarticular fibro-cartilages, hollow on both faces, 

 resemble a biconcave lens. "With regard to the peripheral bands, they are repre- 

 sented by a bundle of longitudinal fibres spread over the surface of the bones, 

 which they envelop in a common sheath. 



2. Intersarral artm/lations. — The sacral vertebrae being fused into one piece 

 — the OS sacrum — there is no occasion to study the true articulations in this 

 region. It may be remarked, however, that the supra-spinous dorso-lumbar liga- 

 ment is continued on the sacral spine, and that there exist between the processes 

 formed by this spine, true interspinous ligaments. 



3. Sdcro-Jumbar artirvlation. — In this articulation, the great thickness of the 

 fibro-cartilage is to be remarked ; and, in addition, that the last lumbar vertebra 

 corresponds with the sacrum not only by its body and articular processes, but 

 also by the oval and slightly concave facets shown on the posterior border of its 

 transverse processes, Avhich are adapted to analogous slightly convex facets on the 

 sides of the base of the sacrum. The bundles of fibres thrown from one bone to 

 another from around these sacro-tra7is?'ersals (real planiform diarthroses) maintain 

 the articular surfaces in contact, and cover, outwardly, the synovial membrane 

 which facilitates their gliding. 



4. Artirulation of the two last lumbar vertphnc. — This is distinguished by the 

 presence, between the transverse processes, of a planiform diarthrosis, like that of 

 the sacro-transversal just noticed. These two articulations are only found in 

 Sohpeds. 



f). Atlo-axoid articulation. — This is so far removed by its conformation and 

 special uses from the other intervertebral articulations, that it will be described 

 as an extrinsic articulation of the head and spine. (See Articulations of the Head.) 



The Movements of the Spine in general. — Each intervertebral articula- 

 tion is the seat of very obscure movements, the separate study of which offers 

 little interest. But these movements, when conjoined with those of the other 

 articulations, result in bending the whole spine in a somewhat marked manner, 

 and producing either the ^flexion, extmsion, or lateral inclination of thLs flexuous 

 column. 



When flexion takes place, the spine is arched upwards, the common inferior 

 ligament is relaxed, the spinous processes separate from one another, and the 

 supra-spinous ligament, becoming very tense, soon imposes limits to this movement. 



Extension is effected Ijy an inverse mechanism, and is checked by the tension 

 of the common inferior ligament and the meeting of the spinous processes. 



