Changes

==='''The trunk is a horizontal beam'''===

==='''The trunk is a horizontal beam'''===

The body of the dog shown in Fig. 9.1 a is represented mechanically by a beam, the vertebral column A–D, 45 cm long with a uniformly distributed load of 0.2 kg.cm–2 (the neck and trunk), and a concentrated load cranially of 2 kg (the head).  The total weight is therefore 11 kg.  With the fore and hindlimbs each represented each by one simple strut and placed as shown at B and C, the opposing reaction forces can be calculated as 7.9 kg for the forelimbs and 3.1 kg for the hindlimbs.  This turns out to be approximately the situation in a real dog in which the weight borne by the forelimb is about twice that borne by the hindlimb.  Since the weight of the hindlimb of the dog is about the same as that of the forelimb, one must conclude that the weight of hindlimb in excess of what is needed for postural support is available for propulsion; in other words the forelimb and the hindlimb of the dog differ in their postural and propulsive roles.  The forelimb supports and balances, the hindlimb pushes.  

The body of the dog shown in Fig. 9.1 a is represented mechanically by a beam, the vertebral column A–D, 45 cm long with a uniformly distributed load of 0.2 kg.cm–2 (the neck and trunk), and a concentrated load cranially of 2 kg (the head).  The total weight is therefore 11 kg.  With the fore and hindlimbs each represented each by one simple strut and placed as shown at B and C, the opposing reaction forces can be calculated as 7.9 kg for the forelimbs and 3.1 kg for the hindlimbs.  This turns out to be approximately the situation in a real dog in which the weight borne by the forelimb is about twice that borne by the hindlimb.  Since the weight of the hindlimb of the dog is about the same as that of the forelimb, one must conclude that the weight of hindlimb in excess of what is needed for postural support is available for propulsion; in other words the forelimb and the hindlimb of the dog differ in their postural and propulsive roles.  The forelimb supports and balances, the hindlimb pushes.  

 

In Fig. 9.1c, muscles preventing bending include (a) the epaxial muscles of the neck and thorax, (b) the hypaxial muscles of the thorax, and (c), the hypaxial muscles of the lumbar region.  Props assisting the action of these muscles and the ligaments shown are (p) the spinous process of the axis, (q) the spinous process of the first thoracic vertebra (together with adjacent spinous processes), (r) the spinous process of the anticlinal vertebra (eleventh thoracic), (s) the sacrum and (t) the costal arch.  

In Fig. 9.1c, muscles preventing bending include (a) the epaxial muscles of the neck and thorax, (b) the hypaxial muscles of the thorax, and (c), the hypaxial muscles of the lumbar region.  Props assisting the action of these muscles and the ligaments shown are (p) the spinous process of the axis, (q) the spinous process of the first thoracic vertebra (together with adjacent spinous processes), (r) the spinous process of the anticlinal vertebra (eleventh thoracic), (s) the sacrum and (t) the costal arch.  

(u) and (v) are the forelimb and hindlimb respectively.  Note that the shape of the vertebral column is opposite to that of the bending moments shown in Fig. 9.1b for the horizontal beam A — D.

(u) and (v) are the forelimb and hindlimb respectively.  Note that the shape of the vertebral column is opposite to that of the bending moments shown in Fig. 9.1b for the horizontal beam A — D.

:::::'''Fig 9.1 Bending in the vertebral column'''  

:::::'''Fig 9.1 Bending in the vertebral column'''  

:::::The trunk of a dog is represented in Fig. 9.1a by a horizontal beam A — D, 45 cm long with a uniformly distributed load of 0.2 kg.cm-1, together with a concentrated load cranially of 2 kg (the head).  The total weight is 11 kg.  With the limbs placed as shown, the opposing reaction forces are 7.9 kg in the forelimb and 3.1 kg in the hindlimb.  Bending moments along the vertebral column are shown graphically in Fig. 9.1b.

:::::The trunk of a dog is represented in Fig. 9.1a by a horizontal beam A — D, 45 cm long with a uniformly distributed load of 0.2 kg.cm-1, together with a concentrated load cranially of 2 kg (the head).  The total weight is 11 kg.  With the limbs placed as shown, the opposing reaction forces are 7.9 kg in the forelimb and 3.1 kg in the hindlimb.  Bending moments along the vertebral column are shown graphically in Fig. 9.1b.

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

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