ANIMAL MECHANICS. 



179 



point, and the insertion of the fibres is a right line Let 0 

 (Fig. 28) denote the origin, and ^4i3the line of insertion. The 

 muscular fibres diverge from the point 0, lying between the 

 lines OA and OB, and each fibre contracts with the same 

 Ibrce, whatever be its length. Draw the line OX bisecting 

 the angle AOB. If the muscular fibres be taken in pairs, 

 making equal angles at opposite sides of OX, the resultant of 

 each pair of fibres will lie along the right line OX, which will 

 therefore be the direction of the resultant of the whole mus- 

 cle ; and since the bisector of the angle AOB divides the base 

 AB into segments AX, XB, proportional to the sides AO 

 and OB, it is easy in all cases to find the point X, in the line 

 of insertion, through which the whole force of the contracting 

 muscle is directed. 



One of the best examples of triangular muscle, with which 

 I am acquainted, is to be found in the biceps femoris of the 

 large Felidw. In a large Lion examined by me, the biceps 

 weighed 27.75 oz. It forms a massive triangular sheet, hav- 

 ing for its origin the highest point of the tuber ischii, and is 

 inserted by strong fascia, continuously, from the middle of 

 the femur, covering the vastus externus, down the entire length 

 of the outer side of the leg, as far as the tendo Achillis, round 

 which it is fastened. 



The total length of the fibres from the origin to the lowest 

 point of insertion was 22.25 inches, and the length of the 

 fibres passing to the highest point of insertion was 8.75 inches. 

 The base of the triangle, when the leg is extended, was 17.25 

 inches. If we divide this length in the proportion of OA to 

 OB, or 22.25 to 8.75, we shall find 



AX = 12.38 inches. 

 BX= 4.87 „ 



This point corresponds exactly with the top of the fibula, so 



