VERTEBRAL COLUMN AS A WHOLE. 85 
VERTEBRAL COLUMN AS A WHOLE. 
When all the vertebre are articulated together, the resulting column displays 
certain characteristic features. The division of the column into a true or movable 
part, comprising the members of the cervical, thoracic, 
and lumbar series, and a false or fixed portion, in- 
cluding the sacrum and coccyx, can now be readily 
recognised. The vertebree are so disposed that the 
centra or bodies form an interrupted column of solid 
parts in front, which constitutes the axis of support 
for the head and trunk; whilst the neural arches 
behind form a canal for the lodgment and protection 
of the spinal cord and _ its membranes. In the 
movable part of the column both the anterior sup- 
porting axis and the neural canal are lable to 
changes in their direction owing to the movements of 
the head and trunk. Like the bodies and neural 
arches the spinous and transverse processes are also 
superposed, and fall in line, forming three series of 
interrupted ridges—one (the spinous) placed centrally, 
the others (the transverse) placed laterally. In this 
way two vertebral grooves are formed which lhe 
between the central and lateral ridges. The floor of 
each groove is formed by the lamine and articular 
processes, and in these grooves are lodged the muscles 
which serve to support and control the movements 
of the column. 
Further, the column so constituted is seen to 
display certain curves in an antero-posterior direction. 
These curves are, of course, subject to very great 
variation according to the position of the trunk and 
head, and can only be satisfactorily studied in a 
fresh specimen; but if care be exercised in the 
articulation of the vertebree, the following character- 
istic features may be observed, assuming, of course, 
that the column is erect and the head so placed that 
the axis of vision is directed towards the horizon. 
There is a forward curve in the cervical region, 
which gradually merges with the backward thoracic 
curve; this becomes continuous below with an 
anterior convexity in the lumbar region, which ends 
more or less abruptly at the union of the fifth 
lumbar with the first sacral vertebra, where the 
sacrum slopes suddenly backwards, causing the 
eolumn to form a marked projection—the  sacro- 
vertebral angle. Below this, the anterior concavity 
of the front of the sacrum is directed downwards as 
well as forwards. Of these four curves, two—the 
thoracic and sacral—are primary, they alone exist 
during foetal life; whilst the cervical and lumbar 
forward curves only make their appearance after 
birth—the former being associated with the extension 
and elevation of the head, whilst the latter is de- 
veloped in connexion with the use of the hind hmb 
in the hyper-extended position, which in man is 
correlated with the assumption of the erect posture ; 
this curve, therefore, only appears after the child has 
Cervical 7 
Thoracic 12 
Lumbar 5 
Sacral 5 
Coecy- 
geal 4-5 
Fic. 65.—VERTEBRAL COLUMN 
FROM THE LEFT SIDE. 
begun to alte For these reasons the cervical and lumbar curves are described 
7 as ‘secondary and compensatory. 
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