250 



ANIMAL MECHANICS. 



AQB, passes through the ninth dorsal vertebra, and is the 

 line of force acting upon the humerus. 



In the position of the Tiger's arm, represented in the 

 figure, the angle, SQX, is 93 0 , and the force of the latissimus 

 dorsi is exerted to flex the arm upon the body at nearly its 

 position of maximum advantage. 



It is important to observe that, when the angle SQX 

 becomes a right angle, the teres major (whose origin is repre- 

 sented at the angle of the scapula, and which is inserted with 

 the latissimus dorsi) acts with its entire force along the 

 bisector QX, and at right angles to SQC; so, that when the 

 latissimus dorsi is acting to the greatest advantage, producing 

 a maximum velocity with a given angle of rotation ; at the 

 same time, its auxiliary muscle, teres major, acts also to the 

 greatest advantage, and exactly in the line of force of the 

 latissimus dorsi. The weights of these muscles in several 

 FelidaB are as follows : — 



Depressors of Arm in the Felidw. 



\ Tiger. 



■ [ - 



Lion. 



Jaguar 

 (female). 



Leopard. 



Latissimus dorsi, 

 Teres major, 



■ 



39 75 oz. 

 "•45 » 



25.50 oz. 

 9-5° » 



4.19 oz. 

 1.68 „ 



8.40 oz. 

 2-6 5 „ 



Total force, 



51.20 oz. 



35 OO oz. 



5.87 oz 



11-05 oz. 



The latissimus dorsi and teres major act upon the humerus, 

 tending to turn it round an axis perpendicular to the plane 

 of the triangular sheet of muscle; but another important 

 muscle assists in this rotation. This muscle is the triceps 

 longus, which takes its origin on the line marked on the pos- 

 terior edge of the scapula, and is inserted, in conjunction with 



