Changes

The trunk of the quadruped is supported on four struts.  If static support of the trunk were their only function, these struts would be straight.  Flexion of the joints of the limb results in a torque exerted by gravity on each joint (Fig 6.3).  Larger mammals, for example the giraffe and the elephant (Fig. 8.2) stand with straight limbs to minimise this torque; smaller animals are able to oppose the torque more easily with muscular force.  Recall that the smaller animal is relatively stronger (Chapter 7).   

The trunk of the quadruped is supported on four struts.  If static support of the trunk were their only function, these struts would be straight.  Flexion of the joints of the limb results in a torque exerted by gravity on each joint (Fig 6.3).  Larger mammals, for example the giraffe and the elephant (Fig. 8.2) stand with straight limbs to minimise this torque; smaller animals are able to oppose the torque more easily with muscular force.  Recall that the smaller animal is relatively stronger (Chapter 7).   

Each joint of the strut needs a mechanism to prevent flexion, especially in large animals like a horse in which a “stay apparatus” is defined; each joint is supported against gravity by a ligamentous or an extremely pennate arrangement of muscles (Fig. 5.8).  Denervation of any of the muscles shown in Fig. 6.3 would reduce the animal's ability to bear weight on the limb. Each of these muscles has been chosen deliberately because it acts over only one joint. This single-joint muscle system is assisted and sometimes superseded by a two-joint muscle system to be described later in this chapter.   

Each joint of the strut needs a mechanism to prevent flexion, especially in large animals like a horse in which a “stay apparatus” is defined; each joint is supported against gravity by a ligamentous or an extremely pennate arrangement of muscles (Fig. 5.8).  Denervation of any of the muscles shown in Fig. 6.3 would reduce the animal's ability to bear weight on the limb. Each of these muscles has been chosen deliberately because it acts over only one joint. This single-joint muscle system is assisted and sometimes superseded by a two-joint muscle system to be described later in this chapter.   

 

:::::'''Fig 8.2 Size effects on mammalian skeletons'''

:::::'''Fig 8.2 Size effects on mammalian skeletons'''

:::::The torque exerted by gravity about the limb joints is reduced in the larger species by increasing the angles of flexion.   

:::::The torque exerted by gravity about the limb joints is reduced in the larger species by increasing the angles of flexion.   

:::::These animals also show a feature of the vertebral column discussed in Chapter 9.  The cat (c) and the rat (d) have cranially directed vertebral spines in the caudal series, with the tenth and twelfth thoracic vertebrae, respectively, anticlinal. The bending imposed on the vertebral column of the elephant (a) and the giraffe (b) necessitates caudally directed lumbar vertebral spines.

:::::These animals also show a feature of the vertebral column discussed in Chapter 9.  The cat (c) and the rat (d) have cranially directed vertebral spines in the caudal series, with the tenth and twelfth thoracic vertebrae, respectively, anticlinal. The bending imposed on the vertebral column of the elephant (a) and the giraffe (b) necessitates caudally directed lumbar vertebral spines.

 

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

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