Changes

=='''The design of the vertebral trunk'''==

=='''The design of the vertebral trunk'''==

==='''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.  

The locomotory apparatus of the trunk is driven by the caudal epaxial muscles, notably the longissimus muscle (Fig. 9.2) and its attachments.  In the species in which the apparatus is well developed, such as rodents, felids and canids, the attachments of the longissimus muscle to the spinous and transverse processes of the caudal thoracic and lumbar vertebrae are functionally strengthened by an angling of these processes away from the direction of tension.  Thus, the transverse processes of the lumbar vertebrae slope cranially and ventrally.  For the spinous processes, the effect is opposite to that seen in the cranial segments of the vertebral column where they slope caudally against the tension in the dorsal stays of the cervicothoracic region (Fig. 9.1 c).  There is therefore an anticlinal vertebra, which represents the changing point (Fig. 8.2).  In species that presumably do not use their vertebral column effectively to lengthen the hindlimb pendulum in locomotion, an anticlinal vertebra is absent.

The locomotory apparatus of the trunk is driven by the caudal epaxial muscles, notably the longissimus muscle (Fig. 9.2) and its attachments.  In the species in which the apparatus is well developed, such as rodents, felids and canids, the attachments of the longissimus muscle to the spinous and transverse processes of the caudal thoracic and lumbar vertebrae are functionally strengthened by an angling of these processes away from the direction of tension.  Thus, the transverse processes of the lumbar vertebrae slope cranially and ventrally.  For the spinous processes, the effect is opposite to that seen in the cranial segments of the vertebral column where they slope caudally against the tension in the dorsal stays of the cervicothoracic region (Fig. 9.1 c).  There is therefore an anticlinal vertebra, which represents the changing point (Fig. 8.2).  In species that presumably do not use their vertebral column effectively to lengthen the hindlimb pendulum in locomotion, an anticlinal vertebra is absent.

We can now proceed to consider the action of the trunk and limbs as used by quadrupeds in performing unusual tasks.

We can now proceed to consider the action of the trunk and limbs as used by quadrupeds in performing unusual tasks.

=='''Locomotion'''==

=='''Locomotion'''==