134 THE ARTICULATIONS. 



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

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



d. Capsules proper to the articular processes (Fig. 81, 5). Each anterior 

 articular process is maintained against the corresponding posterior process 

 by a direct band : this is a peripheric capsule attached around the 

 diarthrodial facets, doubled internally by a synovial membrane which 

 facilitates their gliding, and covered, outwardly, by the insertions of some 

 spinal muscles. These capsules, yellow and elastic in the cervical, are 

 composed of white fibrous tissue in the dorso-lumbar region. Very developed 

 at the neck, in consequence of the thickness of the articular tubercles they 

 envelope, they become reduced, near the middle of the back, to some fibres 

 which cover, outwardly, the diarthrodial facets in contact. 



CHARACTERS PROPER TO SOME INTERVERTEBRAL ARTICULATIONS. 1. Inter- 

 coccygeal and sacro-coccygeal articulations. These are constructed after the 

 same type as the other spinal articulations, except that they are appropriate to 

 the rudimentary state of the vertebrae they unite. The coccygeal bones only 

 come in contact by their bodies, their spinal laminae 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 lense. With regard to the 

 peripheral bands, they are represented by a bundle of longitudinal fibres 

 spread over the surface of the bones, which they envelope in a common sheath. 



2. Intersacral articulations. 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 superspinous dorso- 

 lumbar ligament is continued on the sacral spine, and that there exist be- 

 tween the processes formed by this spine veritable interspinous ligaments. 



3. Sacro-lumbar articulation. 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, which 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- 

 transversals (real planiform diarthroses) maintain the articular surfaces in 

 contact, and cover, outwardly, the synovial membrane which facilitates their 

 gliding. 



4. Articulation of the two last lumbar vertebrse. 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 Solipeds. 



5. 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 the 

 Articulations of the Head.) 



THE MOVEMENTS OF THE SPINE IN GENERAL. Each intervertebral articula- 

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

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

 articulations, result in bending the whole spinal stalk in a somewhat 

 marked manner, and producing either the flexion, extension, or lateral 

 inclination of this flexuons column. 



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

 inferior ligament is relaxed, the spinous processes separate from one 



