Changes

The centre of gravity of the limb is made as proximal as possible (Fig. 8.5 b).  First, the bellies of muscles operating distal joints should lie close to the pivot, transmitting their force by means of long tendons.  This is made easier if propulsive muscles operate mainly about the pivot, rather than by bending the limb distally.  Fig. 8.4 shows that in walking, the limb is indeed an almost rigid pendulum.  If distal joints have fewer axes of movement than proximal joints, the tendinous control apparatus is much simplified.  We saw earlier in this chapter that this is the case.  Also, the muscles responsible for fixing each joint lie proximally to the joint (Fig. 6.3).  An additional advantage of having muscles located proximally is that they are then closer to the heart, thus reducing the length of the vascular channels and thereby improving the efficiency of the blood supply.

The centre of gravity of the limb is made as proximal as possible (Fig. 8.5 b).  First, the bellies of muscles operating distal joints should lie close to the pivot, transmitting their force by means of long tendons.  This is made easier if propulsive muscles operate mainly about the pivot, rather than by bending the limb distally.  Fig. 8.4 shows that in walking, the limb is indeed an almost rigid pendulum.  If distal joints have fewer axes of movement than proximal joints, the tendinous control apparatus is much simplified.  We saw earlier in this chapter that this is the case.  Also, the muscles responsible for fixing each joint lie proximally to the joint (Fig. 6.3).  An additional advantage of having muscles located proximally is that they are then closer to the heart, thus reducing the length of the vascular channels and thereby improving the efficiency of the blood supply.

Secondly, the structures forming a friction contact with the ground must be light, whether they be naturally grown keratin, or metal shoes.  The ungulate (hooved animal) evolved for this reason.

Secondly, the structures forming a friction contact with the ground must be light, whether they be naturally grown keratin, or metal shoes.  The ungulate (hooved animal) evolved for this reason.

Thirdly, the number of digits can be reduced, effectively to two in many artiodactyls (even toed ungulates) and to one in some perissodactyls (odd toed ungulates).  A single structure is stronger than a paired structure of the same weight and length.  Thus even in artiodactyls, fusion of the metapodial segment often occurs.  Such a reduction in digits enhances cursorial (Latin: cursor, runner) ability and sacrifices the ability to use hands for specialised procedures.  

Thirdly, the number of digits can be reduced, effectively to two in many artiodactyls (even toed ungulates) and to one in some perissodactyls (odd toed ungulates).  A single structure is stronger than a paired structure of the same weight and length.  Thus even in artiodactyls, fusion of the metapodial segment often occurs.  Such a reduction in digits enhances cursorial (Latin: cursor, runner) ability and sacrifices the ability to use hands for specialised procedures.  

:::::'''Fig 8.5 Improvements to pendulum design'''

:::::'''Fig 8.5 Improvements to pendulum design'''

:::::Modifications to a basic pendulum (a) that increase the natural frequency of oscillation (b, e) or the distance moved by the tip in each swing (c, d).   

:::::Modifications to a basic pendulum (a) that increase the natural frequency of oscillation (b, e) or the distance moved by the tip in each swing (c, d).   

:::::'''Fig 8.6 Phylogenetic elongation of the distal end of the mammalian limb'''  

:::::'''Fig 8.6 Phylogenetic elongation of the distal end of the mammalian limb'''  

 

==='''Balancing the pendulum'''===  

==='''Balancing the pendulum'''===