Vertebral Column 15 



It is evident that a forward bending of a part of the column will lead to separation 

 between the corresponding laminae and spines, and thus we find that the lamin;e are 

 connected with those above and below by interlaminar ligaments (ligamenta subflava) 

 composed of almost pure elastic tissue ; these are prolonged back between the spi 

 as inter spinous ligaments, best developed in the lumbar region and only represented 

 higher up by a fibrous or areolar web that makes markings on the bones. At the top 

 of the column, where the movements of the head demand a greater range of motion 

 between the first two vertebrae and the skull, the interlaminar ligaments become 

 modified and represented by thickened areolar tissue : in this case the functions of 

 ligaments are performed by the short muscles that connect the top of the column and 

 the skull. The interspinous ligaments below the level of the 2nd c.v. may be looked on 

 as simply the thickened areolar sheaths of the interspinous muscles, which also act as 

 extensible ligaments limiting the excursus of the spines. 



In the same way the separation of the transverse processes in lateral flexion of the 

 column is met by intertransverse muscles modified partly into tendinous fibres ; but 

 true intertransverse ligaments other than these are not easily found, save in a part of 

 the dorsal region in which some fibres of the costo-transverse series appear to be also 

 in part intertransverse. 



Looking again at the back of the column, it is seen that the imbricated laminae 

 and spines hide the contained spinal canal to such an extent that it is usually only 

 possible to see into it easily in the lower two or three lumbar intervals. It is evident, 

 therefore, that here the ligamenta subflava are most visible, completing the covering 

 of the canal, and this region is chosen of necessity for the operation of inserting a 

 needle into the membranes of the cord to draw off cerebro-spinal fluid : the proceeding 

 is helped by forward flexion of the spine, which is a movement most easily carried out 

 in this region. 



The movements between the parts of the different vertebrae may be shortly 

 summed up : the bodies, being in and round the centre of motion, move least, and 

 the various processes move more, in proportion as they are far away from the body in 

 the plane of the particular movement. 



The spinal cord and its membranes, lying deep to the neural arch which moves 

 away from or to its neighbours in flexion or extension, obtains the utmost possible 

 amount of freedom from movement by having no attachment to the arches but being 

 held to the back of the column of bodies, both by the irregular and slight adhesion of 

 the dura mater to the posterior common ligament and by the attachment of its nerves 

 to the pedicles and discs through their sheaths of dura mater. 



CERVICAL VERTEBRAE. 



The drawing of a cervical vertebra in Fig. 9 would represent, with minor modifi- 

 cations, the general appearance of any member of this series from the third to the sixth 

 inclusive ; but the type has been distinctly altered in the upper and lower vertebrae 

 of the region. 



In the first two vertebrae the alteration is remarkable, in association with the 

 necessity for providing free movement of the head on the column, but it is slighter in 

 the seventh segment and connected with the change from the physical conditions of 

 the cervical to those of the dorsal region. 



The first vertebra is termed the Atlas, because it supports the globe of the skull : 

 the second is called the Axis, because it forms the pivot round which the atlas turns 

 and carries the skull. 



