INTERCENTRAL ARTICULATIONS — INTERNEURAL ARTICULATIONS 



173 



vertebral column or a considerable part of it. The joints between the atlas and 

 axis and between the former and the skull require separate consideration. 



INTERCENTRAL ARTICULATIONS 



These are amphiarthroses, formed by the junction of the extremities of the 

 bodies of adjacent vertebrae. The articular surfaces in the cervical region consist 

 of a cavity on the posterior end of the body of the anterior vertebra, and a cor- 

 responding convexity or head of the succeeding vertebra. In the other regions the 

 surfaces are much flattened. The uniting media are: 



1. The intervertebral fibro-cartilages (Fibrocartilagines intervertebrales). 

 Each of these is a disc which fits into the space between the bodies of two adjacent 

 vertebrae, to which it is intimately attached. The discs are thinnest in the middle 

 of the thoracic region, thicker in the cervical and lumbar regions, and thickest in 

 the coccygeal region. Each consists of a dense fibrous peripheral part (Annulus 

 fibrosus), and a soft pulpy 



Supraspi- 



iiuus liga- 



meyit 



139. — Saoittai. Section of Last Two Thoracic and First 

 Lumbar Vkrtebr.e, showixc Ligaments and Spinal Cord 

 (Medulla). (After Schmaltz, Atlas d. Anat. d. Pferdes.) 



central part (Nucleus pul- 

 posus). 



The fibrous ring consists 

 of laminsp of fil)rous tissue and 

 fibro-cartilage, which pass ob- 

 liquely between the two verte- 

 bra^ and alternate in direction, 

 forming an X-shaped arrange- 

 ment. The central part of the 

 ring is largely cartilaginous, and 

 gradually assumes the character 

 of the pulpy center. The latter 

 is very elastic and is compressed, 

 so that it bulges considerably 

 from the surface of sections; it 

 consists of white and elastic 

 fibers, connective-tissue cells, 

 and peculiar clear, transparent yig 

 cells of various sizes. It is a 

 remnant of the notochord. 

 There are joint cavities in the 

 cervical intercentral joints, and 



in those between the last cervical and the first thoracic, and between the last lumbar and the 

 sacrum. In the latter the cavity is coextensive with the extremities of the bodies; in the former, 

 it is usually not so extensive. 



2. The inferior common ligament (Ligamentum longitudinale ventrale) lies 

 on the ventral surface of the bodies of the vertel)rae and the intervertebral fibro- 

 cartilages, to which it is firmly attached. It l^egins aliout the fourteenth or fifteenth 

 thoracic vertebra, and is at first a narrow, thin band. Further back it becomes 

 gradually thicker and wider, and terminates on the pelvic surface of the sacrum 

 by spreading out and blending with the periosteum. It is strongest in the lumbar 

 region, where the tendons of the crurp of the diaphragm fuse with it. 



3. The superior common ligament (Ligamentum longitudinale dorsale) lies on 

 the floor of the vertel^ral canal from the dens or odontoid process to the sacrum. 

 It is narrow over the middles of the vertebral bodies, and widens over the inter- 

 vertebral fibro-cartilages, to which it is very firmly attached. 



This ligament is in relation with the spinal veins on either side, and in the middle of each 

 vertebra a transverse anastomotic branch passes under the ligament. 



INTERNEURAL ARTICULATIONS 

 Each typical vertebra presents two pairs of articular processes, which form 

 diarthroses with the two adjacent vertebrae. The articular surfaces are extensive, 



