252 ANIMAL MECHANICS. 



in each contraction of the group of muscles, with those already 

 given, we find — 



Ratio of Depressors of Arm to Extensors of Forearm in 

 the Felidee. 



Tiger. Lion. Jaguar (female). Leopard. 



0.88 0.80 0.76 0.80. 



With respect to the action of the triceps and its assistants 

 upon the elbow joint, the following considerations are of in- 

 terest. The triceps, will produce, in conformity with Pro- 

 position B. its maximum effect upon the forearm, turning 

 round the centre C (Fig. 66), when the quadrilateral OSC1 

 comes into the position in which the line of force of the triceps 

 01 is at right angles to the line CI In this position of the 

 quadrilateral, the right line Ci, drawn from the point C to 

 meet the circle I'll", becomes a tangent to that circle. 



It is evident from the figure, that the angle OIC becomes 

 a right angle at the same time as the angles SQX and SOI ; 

 and therefore, that in the position of maximum effect of all 

 the muscles acting on the shoulder and elbow joints, the lines 

 SO and CI become parallel to each other, and are both at 

 right angles to the direction of the triceps 01. 



From the preceding facts, it is plain that the triceps is 

 intended to co-operate with the latissimus dorsi and teres major ; 

 and in point of fact, in the Tiger it co-operates with these 

 muscles, when both they and it are placed in their relative 

 positions of maximum effect upon the rotations, round both 

 the shoulder and elbow joints. 



I have repeatedly watched the back stroke of the arm in 

 all the large Felidse, and am unable to perceive the slightest 

 difference in the time of action of the elbow and shoulder 

 joints in the Tiger, Jaguar, or Panther; in the Lion it appears 



