Changes

==='''Balancing the pendulum'''===  

==='''Balancing the pendulum'''===  

The distal limb segments should be as long as possible (Fig. 8.5 c).  This is achieved either by actual elongation of the distal segments relative to the proximal segments (Figs. 8.2 and 8.6), or by incorporation of the distal segments into the pendulum by running on the tip of the toes (Fig. 8.6).

The distal limb segments should be as long as possible (Fig. 8.5 c).  This is achieved either by actual elongation of the distal segments relative to the proximal segments (Figs. 8.2 and 8.6), or by incorporation of the distal segments into the pendulum by running on the tip of the toes (Fig. 8.6).

 

The pivot of the pendulum should be as proximal as possible (Fig. 8.5 d).  Some mammals have a complete bony pectoral girdle, which compels the forelimb to pivot from the shoulder joint (Fig. 8.7 a).  A cursorial adaptation has been the reduction of bony elements of the pectoral girdle, freeing the scapula and allowing the limb to pivot from a point proximal to the shoulder (Figs. 5.3, 8.3 b, 8.4 b, 8.7 b).  The dorsal border of the scapula moves cranially in limb retraction (Fig. 5.3).  This enables muscles connecting the scapula to the head and neck (Mm rhomboideus, trapezius and serratus ventralis), and movements of the neck, to assist retraction.  In galloping, in which the footfalls of the forelimb closely follow one another, the head is lowered during retraction and raised during protraction.   

The pivot of the pendulum should be as proximal as possible (Fig. 8.5 d).  Some mammals have a complete bony pectoral girdle, which compels the forelimb to pivot from the shoulder joint (Fig. 8.7 a).  A cursorial adaptation has been the reduction of bony elements of the pectoral girdle, freeing the scapula and allowing the limb to pivot from a point proximal to the shoulder (Figs. 5.3, 8.3 b, 8.4 b, 8.7 b).  The dorsal border of the scapula moves cranially in limb retraction (Fig. 5.3).  This enables muscles connecting the scapula to the head and neck (Mm rhomboideus, trapezius and serratus ventralis), and movements of the neck, to assist retraction.  In galloping, in which the footfalls of the forelimb closely follow one another, the head is lowered during retraction and raised during protraction.   

The pivot is moved into the vertebral column in animals that gallop with a flexible column.  This applies to forelimbs and hindlimbs, and not only elongates the pendulum but enables axial muscles to participate in propulsion (Fig. 5.3).

The pivot is moved into the vertebral column in animals that gallop with a flexible column.  This applies to forelimbs and hindlimbs, and not only elongates the pendulum but enables axial muscles to participate in propulsion (Fig. 5.3).

:::::'''Fig 8.7 Adaptation of the pectoral girdle in a cursorial mammal'''

:::::'''Fig 8.7 Adaptation of the pectoral girdle in a cursorial mammal'''

:::::In the echidna (a), the clavicle and the coracoid form two complete bony bridges between the scapula and the sternum.  In the dog (b), only remnants of these bridges remain, represented by the coracoid process of the scapula and a fibrous or occasionally ossified tendinous intersection within the brachiocephalicus muscle.  The pivot for the forelimb can be located proximally to the shoulder.

:::::In the echidna (a), the clavicle and the coracoid form two complete bony bridges between the scapula and the sternum.  In the dog (b), only remnants of these bridges remain, represented by the coracoid process of the scapula and a fibrous or occasionally ossified tendinous intersection within the brachiocephalicus muscle.  The pivot for the forelimb can be located proximally to the shoulder.

==='''Reciprocating the pendulum'''===  

==='''Reciprocating the pendulum'''===