700 ON FORM AND MECHANICAL EFFICIENCY [ch. 



illustrated to the plan of the quadrupedal skeleton ; for the main 

 compression-member almost exactly recalls the form of the verte- 

 bral column, while the main tension-member, though not so 

 closely similar to the supraspinous and nuchal ligaments, corre- 

 sponds to the plan of these in a somewhat simplified form. 



Fig. 345. A two-armed cantilever of the Forth Bridge. Thick lines, com- 

 pression-members (bones); thin lines, tension-members (ligaments). 



We may now pass without difficulty from the two-armed 

 cantilever supported on a single pier, as it is in each separate 

 section of the Forth Bridge, or as we have imagined it to be in 

 the forequarters of a horse, to the condition which actually exists 

 in that quadruped, where a two-armed cantilever has its load 

 distributed over two separate piers. This is not precisely what 

 an engineer calls a "continuous" girder, for that term is applied 

 to a girder which, as a continuous structure, crosses two or more 

 spans, while here there is only one. But nevertheless, this girder 



c 



Fig. .346. 



is effectively continuous from the head to the tip of the tail ; and 

 at each point of support {A and B) it is subjected to the negative 

 bending-moment due to the overhanging load on each of the 

 projecting cantilever arms AH and BT. The diagram of bending- 

 moments will (according to the ordinary conventions) lie below 



