Changes

Apart from the joint between the first two cervical vertebrae, the intervertebral joints are not synovial joints.  It is important that joints in a column under compression should be able to distribute pressure evenly over the opposing surfaces of the vertebral bodies, regardless of the angle of the joint.  Intervertebral movement and even pressure distribution are achieved hydrostatically by the nucleus pulposus between each body (Figs. 9.2, 9.3).  The change in shape of this mucoprotein gel with movement of the joint is accommodated by the annulus fibrosis, a lamellar arrangement of collagen fibres.  The lamellae pass from vertebra to vertebra with their fibres crossing each other obliquely.  They are therefore constructed to withstand the tensile stress imposed by the bending of the vertebral column, and also to prevent rupture of the nucleus pulposus.  The mechanical and morphological concept suggested by the term intervertebral disc is misleading.   

Apart from the joint between the first two cervical vertebrae, the intervertebral joints are not synovial joints.  It is important that joints in a column under compression should be able to distribute pressure evenly over the opposing surfaces of the vertebral bodies, regardless of the angle of the joint.  Intervertebral movement and even pressure distribution are achieved hydrostatically by the nucleus pulposus between each body (Figs. 9.2, 9.3).  The change in shape of this mucoprotein gel with movement of the joint is accommodated by the annulus fibrosis, a lamellar arrangement of collagen fibres.  The lamellae pass from vertebra to vertebra with their fibres crossing each other obliquely.  They are therefore constructed to withstand the tensile stress imposed by the bending of the vertebral column, and also to prevent rupture of the nucleus pulposus.  The mechanical and morphological concept suggested by the term intervertebral disc is misleading.   

==='''This rigid beam can be flexible'''  

==='''This rigid beam can be flexible'''===

In the dog, the maximum movement occurs between the segments around the tenth and the eleventh thoracic vertebrae.  These segments are the most vulnerable to the injury of intervertebral structures.  This is especially so in dogs with short legs which must use their vertebral column to a greater extent for propulsion than long legged dogs.

In the dog, the maximum movement occurs between the segments around the tenth and the eleventh thoracic vertebrae.  These segments are the most vulnerable to the injury of intervertebral structures.  This is especially so in dogs with short legs which must use their vertebral column to a greater extent for propulsion than long legged dogs.

The flexibility of the vertebral column varies between species.  A galloping horse maintains an almost rigid back (Fig. 9.4 a).  This is also true for some of the fastest terrestrial animals, the gazelles and antelopes, some of which are small (Fig. 9.4 b).  This is in contrast with the cheetah (Fig. 9.4 c).  The big cats, which have flexible vertebral columns, spend little of their time standing, as compared with herbivores of equivalent size, which have more rigid columns.  The axial muscles of herbivores are presumably more postural in function than those of carnivores and the smaller animals.

The flexibility of the vertebral column varies between species.  A galloping horse maintains an almost rigid back (Fig. 9.4 a).  This is also true for some of the fastest terrestrial animals, the gazelles and antelopes, some of which are small (Fig. 9.4 b).  This is in contrast with the cheetah (Fig. 9.4 c).  The big cats, which have flexible vertebral columns, spend little of their time standing, as compared with herbivores of equivalent size, which have more rigid columns.  The axial muscles of herbivores are presumably more postural in function than those of carnivores and the smaller animals.

:::::'''Fig 9.4 Flexibility of the vertebral column in galloping animals'''

:::::'''Fig 9.4 Flexibility of the vertebral column in galloping animals'''

 

==='''The vertebral column in locomotion'''===

==='''The vertebral column in locomotion'''===