Changes

==='''How each limb is attached to the trunk'''===

==='''How each limb is attached to the trunk'''===

The most stable quadrupedal posture results from splaying the limbs.  However, even in giraffes the attachments of the limbs to the trunk are so designed that they can maintain the basically unstable equilibrium of a heavy load supported on nearly vertical piles.  In the hindlimb, the proximal segment of the limb, the hip bone, is fused to the vertebral column and to the contralateral segment (Fig. 8.3 a).  The effective postural attachment for the hindlimb is therefore the hip joint.  This spherical joint allows flexion–extension, adduction–abduction and rotation freely.  Postural control is therefore dependent on muscles fixing the joint, particularly to prevent abduction and flexion.  That muscles are necessary for the stabilisation of the hip is evident when you see a weakened cow trying to stand on smooth concrete.  

The most stable quadrupedal posture results from splaying the limbs.  However, even in giraffes the attachments of the limbs to the trunk are so designed that they can maintain the basically unstable equilibrium of a heavy load supported on nearly vertical piles.  In the hindlimb, the proximal segment of the limb, the hip bone, is fused to the vertebral column and to the contralateral segment (Fig. 8.3 a).  The effective postural attachment for the hindlimb is therefore the hip joint.  This spherical joint allows flexion–extension, adduction–abduction and rotation freely.  Postural control is therefore dependent on muscles fixing the joint, particularly to prevent abduction and flexion.  That muscles are necessary for the stabilisation of the hip is evident when you see a weakened cow trying to stand on smooth concrete.  

 

The proximal segment of the forelimb, the scapula, has no direct bony attachment to the vertebral column.  Posture is maintained by the transmission of the gravitational force not through bone, but through the muscle fibres of m. serratus ventralis, which carries the trunk between the two forelimb struts as a sling (Fig. 8.3 b).  Since there is no bony joint, all axes of movement are possible, and all extrinsic muscles of the forelimb are needed to stabilise the attachment of the prop.  In the transverse plane, in particular mm rhomboideus and trapezius act as abductors and m. pectoralis superficialis acts as an adductor of the limb.  

The proximal segment of the forelimb, the scapula, has no direct bony attachment to the vertebral column.  Posture is maintained by the transmission of the gravitational force not through bone, but through the muscle fibres of m. serratus ventralis, which carries the trunk between the two forelimb struts as a sling (Fig. 8.3 b).  Since there is no bony joint, all axes of movement are possible, and all extrinsic muscles of the forelimb are needed to stabilise the attachment of the prop.  In the transverse plane, in particular mm rhomboideus and trapezius act as abductors and m. pectoralis superficialis acts as an adductor of the limb.  

:::::'''Fig 8.3 Pivots for the limbs of the dog'''

:::::'''Fig 8.3 Pivots for the limbs of the dog'''

:::::Cranial view of the articulations between the pelvic girdle (a) and the pectoral girdle (b). The level of each pivot is shown with arrows.  Detachment of the scapula from a bony connection with the trunk raises the pivot to the level of entry of nerves and blood vessels to the limb.

:::::Cranial view of the articulations between the pelvic girdle (a) and the pectoral girdle (b). The level of each pivot is shown with arrows.  Detachment of the scapula from a bony connection with the trunk raises the pivot to the level of entry of nerves and blood vessels to the limb.