256 



ANIMAL MECHANICS 



be rotated through a considerable angle, without altering the 

 length of the fourth side, 01 ; and, consequently, without 

 lengthening or shortening the triceps lovgus. 



In the forward direction, the arm SC may be moved into 

 the position, SC", such that 0/plus IC shall be equal to the 

 right line, 01" C"', and in the backward direction, the arm 

 may be moved into the position, SCT, such that SC plus CI 

 shall be equal to the right line, SC'T. While the arm is 

 moved from SO to SC", through an angle of 65 0 , the fibres of 

 the triceps muscle, 01, are neither lengthened nor shortened ; 

 if the arm be brought farther forward than SC", its fibres will 

 be stretched, and the muscle provoked to contract itself; and 

 the arm cannot be brought farther backward than the position 

 SC, unless the fibres of the triceps be shortened. 



(c). Latissimus dorsi (Albatross). 



Fig. 6j. 



The latissimus dorsi of 

 the wing of the Alba- 

 tross, (one half natural 

 size) is shown in Fig. 67, 

 in which S, the socket 

 of the humerus, is 2.20 

 inches distant from 0, 

 the point of insertion of 

 the muscle, which is 

 triangular in shape, its 

 extreme fibres making 

 an angle of 51 0 with 

 each other. In the 

 mean position of the 

 wing, in the dead bird, 

 the angle SOX, con- 

 tained between OS and 



OX, the bisector of the musular fibres is 86°. During life, 



