Changes

==='''Forces along the beam'''===

==='''Forces along the beam'''===

The skeleton of the trunk is a row of separate bones, the vertebral column, on its own hardly a stable bridge.  Its rigidity is maintained to a large extent by a compressive force produced in the massive muscle surrounding the column (Fig. 9.2).  As a bridge, therefore, this structure is comparable to prestressed concrete.  We have already seen that the trabecular network is oriented axially within the vertebral bodies, to resist the tensile stress (Fig. 3.2).  When the axial muscles are relaxed as during anesthesia, the vertebral column is no longer rigid.   

The skeleton of the trunk is a row of separate bones, the vertebral column, on its own hardly a stable bridge.  Its rigidity is maintained to a large extent by a compressive force produced in the massive muscle surrounding the column (Fig. 9.2).  As a bridge, therefore, this structure is comparable to prestressed concrete.  We have already seen that the trabecular network is oriented axially within the vertebral bodies, to resist the tensile stress (Fig. 3.2).  When the axial muscles are relaxed as during anesthesia, the vertebral column is no longer rigid.   

Rigidity of the vertebral column is attained also by the supraspinous and dorsal and ventral longitudinal ligaments (Figs. 9.2 and 9.3) and by the shape of the synovial intervertebral (zygapophyseal) joints.  

Rigidity of the vertebral column is attained also by the supraspinous and dorsal and ventral longitudinal ligaments (Figs. 9.2 and 9.3) and by the shape of the synovial intervertebral (zygapophyseal) joints.  

:::::'''Fig 9.2 Transverse section of a pig at the thoracolumbar junction'''  

:::::'''Fig 9.2 Transverse section of a pig at the thoracolumbar junction'''  

 

==='''The effect of gravity on the beam'''===  

==='''The effect of gravity on the beam'''===