Changes

::Compare the angle of the hock joint when the limb bears weight, and when not weight-bearing.  The passive tissues supporting this joint store energy in A and release it in B.  At hopping speeds of between 10 and 35 km/h, kangaroo locomotion is remarkably efficient.  This is due to the almost 100% resilience of the elastic support of the hock joint.  

::Compare the angle of the hock joint when the limb bears weight, and when not weight-bearing.  The passive tissues supporting this joint store energy in A and release it in B.  At hopping speeds of between 10 and 35 km/h, kangaroo locomotion is remarkably efficient.  This is due to the almost 100% resilience of the elastic support of the hock joint.  

[[File:QMSection2.6.png|thumb|Fig. 2.6 Elastin in the nuchal ligament of a sheep]]

[[File:QMSection2.6.png|thumb|'''Fig. 2.6 Elastin in the nuchal ligament of a sheep''']]

::'''Fig. 2.6 Elastin in the nuchal ligament of a sheep'''

::'''Fig. 2.6 Elastin in the nuchal ligament of a sheep'''

Several biological materials show rubbery elasticity.  In vertebrates, elastin is present in thin strands in loose connective tissue, providing the extreme elasticity of such tissues as the dermis.  It predominates in the middle coat of the wall of large arteries and in the nuchal ligament of herbivores (Figs. 2.6, 2.7).  It is not fibrous, but consists of thin homogeneous strands.  Its elasticity is similar to that of lightly vulcanised rubber.     

Several biological materials show rubbery elasticity.  In vertebrates, elastin is present in thin strands in loose connective tissue, providing the extreme elasticity of such tissues as the dermis.  It predominates in the middle coat of the wall of large arteries and in the nuchal ligament of herbivores (Figs. 2.6, 2.7).  It is not fibrous, but consists of thin homogeneous strands.  Its elasticity is similar to that of lightly vulcanised rubber.     

[[File:QMSection2.7.png|thumb|Fig 2.7 A grazing cow]]

[[File:QMSection2.7.png|thumb|'''Fig 2.7 A grazing cow''']]

::'''Fig.2.7 A grazing cow.'''  

::'''Fig.2.7 A grazing cow.'''  

''Fibrous elasticity:'' Polymeric molecules derive their elasticity by being arranged partly in ordered patterns to form crystalline regions, and partly with a random arrangement in amorphous regions.  Examples of elastic materials of this kind include synthetic textiles like nylon and polyester, and natural ones like silk.  Collagen, the main component of the passive musculoskeletal system, also has polymeric molecules, with the crystalline part composed of aligned and cross-linked molecules, appearing as fibrils (Figs. 2.8, 2.9).  The molecules are aligned in a specific direction to form fibrils.  

''Fibrous elasticity:'' Polymeric molecules derive their elasticity by being arranged partly in ordered patterns to form crystalline regions, and partly with a random arrangement in amorphous regions.  Examples of elastic materials of this kind include synthetic textiles like nylon and polyester, and natural ones like silk.  Collagen, the main component of the passive musculoskeletal system, also has polymeric molecules, with the crystalline part composed of aligned and cross-linked molecules, appearing as fibrils (Figs. 2.8, 2.9).  The molecules are aligned in a specific direction to form fibrils.  

[[File:QMSection2.8.png|thumb|Fig. 2.8 Molecular structure of collagen in a tendon, diagrammatic]]

[[File:QMSection2.8.png|thumb|'''Fig. 2.8 Molecular structure of collagen in a tendon, diagrammatic''']]

'''The significance of collagen'''

'''The significance of collagen'''

::f., as seen grossly in a large animal.  

::f., as seen grossly in a large animal.  

[[File:QMSection2.9.png|thumb|Fig. 2.9 Molecular structure of collagen in a tendon, diagrammatic ]]

[[File:QMSection2.9.png|thumb|'''Fig. 2.9 Collagen structure, viewed electron-microscopically''' ]]

::'''Fig. 2.9 Molecular structure of collagen in a tendon, diagrammatic'''

::'''Fig. 2.9 Collagen structure, viewed electron-microscopically'''

::Magnification x25,000.

::Magnification x25,000.

::Lateral accessoriometacarpal ligament of a horse.  

::Lateral accessoriometacarpal ligament of a horse.