8 THE SUPERIOR EXTREMITY 



surface of the acromion of the scapula. When the upper 

 limb is moved, however, the joint can easily be detected. 

 In strong contrast to the inconspicuous acromio-clavicular 

 joint is the sterno-clavicular joint, where the medial end of the 

 clavicle can be felt as a marked projection, although it is 

 masked, to the eye, by the sternal part of the sterno-cleido- 

 mastoid muscle which causes the ridge-like prominence at the 

 side of the neck as it extends from the sternum and clavicle to 

 the skull behind the ear. Place the index finger in \hzjugular 

 notch on the upper border of the manubrium sterni, between 

 the clavicles, and carry it downwards, along the middle of 

 the sternum, in the interval between the attachments of the 

 great pectoral muscles. The portion of the sternum un- 

 covered by the two greater pectoral muscles is narrow above, 

 but it widens out below, and as the finger passes along it a 

 prominent ridge will be felt. The ridge marks the junction 

 of the manubrium sterni with the body of the sternum, and 

 also the level at which the costal cartilages of the second 

 ribs join the sternum. It is easily felt and can often be seen. 

 It is, therefore, an excellent landmark, indicating the positions 

 of the second pair of ribs, from which the counting of the other 

 ribs should always commence. At the lower end of the body of 

 the sternum, the finger, as it is carried downwards, will sink 

 suddenly into a depression, between the cartilages of the 

 seventh pair of ribs, and rest against the xiphoid process of 

 the sternum. The depression is termed the infrasternal fossa, 

 or pit of the stomach. The costal arches, below the first, 

 are easily recognised, but the first rib lies deeply under the 

 clavicle, and can be felt only in front, at its junction with 

 the manubrium sterni. The arm should now be abducted 

 (i.e. carried laterally from the trunk), when the hollow of 

 the axilla and the two rounded folds, which bound it 

 in front and behind, will be brought into view. The 

 anterior fold of the axilla is formed by the lower border of 

 the pectoralis major, and to a small extent also by the lower 

 border of the pectoralis minor. The posterior fold, which is 

 formed by the latissimus dorsi as it winds round the teres 

 major muscle, is carried downwards to a lower level than the 

 anterior fold. This, as will be seen later, is an important 

 point in connection with the anatomy of the axilla. If the 

 finger is pushed upwards into the axilla the globular head of 

 the humerus will be felt, when the arm is rotated. One other 



