136 CLINICAL APPLIED ANATOMY. 



sternal. One of these may be wasted without the other. The 

 action of the two parts of the muscle is demonstrated as follows. 

 If the arm is advanced in the horizontal plane and then carried 

 towards the mid-line of the body against resistance, both parts 

 of the muscle stand out. If, in this position, the arm is raised 

 against resistance, only the clavicular fibres contract ; if it is 

 depressed against resistance only the costo-sternal fibres are in 

 action. The sternal part is frequently involved in the muscular 

 dystrophies, and wasting of the latissimus dorsi is often associated. 

 The clavicular part is usually affected together with the serratus 

 magnus. Wasting of the clavicular fibres of the pectoralis major 

 gives rise to subclavicular depressions. 



The latissimus dorsi retracts and adducts the humerus, the 

 arm being carried across the back as in the action of placing the 

 hand in the coat-tail pocket. The muscle can be made to stand 

 out by executing this movement against resistance. By palpating 

 the posterior axillary fold the muscle can also be felt to contract 

 during coughing or sneezing. Its contracture during these 

 expiratory efforts is probably for the purpose of fixing the lower 

 ribs in order that the external oblique muscle, which rises from 

 them, may compress the abdomen. 



The biceps is a flexor and supinator of the forearm. When 

 supination without flexion is required this muscle is antagonised 

 by the triceps. 



The brachialis anticus is a flexor of the elbow. 



Wasting of the triceps, biceps and brachialis anticus produces 

 the slender cylindrical arm seen in muscular dystrophy. 



The supinator longus or brachio-radialis flexes the elbow and 

 is usually said to always bring the thumb uppermost from any 

 position. It is, however, a pure flexor without any pronator or 

 supinator action. Its fleshy belly at the outer side of the ante- 

 cubital fossa is easily recognised when the forearm is flexed 

 against resistance. 



The intrinsic muscles of the hand. The dorsal interossei 

 abduct and the palmar interossei adduct the extended fingers 

 away from or towards a line running through the middle finger. 



