ARTICULATIONS OF THE VERTEBRAL COLUMN. 



121 



manner of a wheel rolling on the ground, with or without this change of place being 

 accompanied by gliding motion. 



In the various joints provided with synovial cavities, the cartilaginous surface of 

 the bones are so formed as usually to be in close apposition or contact ; but it would 

 appear that in certain positions they are not entirely so, and it can scarcely be 

 doubted that when the surfaces are separated to any extent, doubling of the synovial 

 membrane, or fatty processes connected with it and placed in the immediate 

 vicinity of the joint, contribute to fill up the vacuity. There are even instances in 

 which it would appear that the separation of the surfaces must be considerable, as in 

 the case of the patella, more especially in complete extension of the knee. 



ARTICULATIONS OF THE TRUNK AND HEAD. 



ARTICULATIONS OF THE VERTEBRAL COLUMN. 



The movable vertebrae are connected together by elastic discs interposed 

 between the bodies ; by synoviul joints between the articulating processes ; 

 and by ligaments. 



Fig. 107. A LUMBAR VERTEBRA, SEEN FROM 



ABOVE, WITH PART OF THE INTERVERTEBRAL 

 DlSC ADHERING TO THE BODY. A 



1, 1, the concentric arrangement of the fibrous 

 laminae ; 2, the central soft cartilaginous or 

 gelatinous substance. 



The intervertebral discs are plates of 

 composite structure placed one between 

 the bodies of each pair of vertebrae from 

 the axis to the base of the sacrum. Each 

 is composed of a laminar part externally, 

 and of a pulpy substance in the centre. 



The laminar part forms more than 

 half of the mass, and consists of con- 

 centric laminae of fibre-car tilage and fibrous tissue alternating one with 

 another. These laminse are not quite vertical, for if a vertical section of a 

 disc be made, a certain number of the layers nearest to the circumference of 

 the disc will be seen bulging outwards, while others situated more deeply 

 and less closely compacted together are convex towards the centre ; and 



Fig. 108. 



Fig. 108. VERTICAL ANTERO- 

 POSTKRIOR SECTION THROUGH 

 TWO LUMBAR VERTEBRAE, SHOW- 

 ING THE ARRANGEMENT OF THE 



INTERVERTEBRAL Disc. 



1, 1, the fibrous oblique bauds, 

 which are curved outwards; 2, 

 those which are curved inwards; 

 3, the central soft cartilaginous or 

 gelatinous substance : the capsule 

 of the joint between the articular 

 processes is represented. 



when the spine is bent in 

 any direction, the curves of 

 the different layers are aug- 

 mented on the side towards which the column is inclined. The in- 

 dividual layers consist chiefly of fibres extending obliquely between the 



