166 



ANIMAL MECHANICS. 



sultant will pass through the centres of gravity of the areas 

 marked on the bones by the origin and insertion of the fibres. 



Good examples of the Direct Prismatic muscle may be found 

 in the sartorius and omo-atlantic muscles of various animals. 



Fig. 23. 



Rhomboidal Muscles. —If the two bars, A A and BB, be 

 held, as in Fig. 23, so that the fibres joining them are oblique 

 to the bars, we have the Bhomboidal muscle of Borelli. In 

 this case the resultant force is also 

 F=nf; 



but as it acts in the right line ab, which is oblique to the bars 

 AA and BB, it may be resolved into two forces at each bar, 

 viz., bH, bV, and aH', aV'\ of these forces, bH and aH' act 

 parallel to the bars, and tend to bring them into the position 

 of the prismatic muscle ; the other forces &Fand aV tend to 



