2l6 



APPLIED ANATOMY. 



THE UPPER EXTREMITY. 



called the axial 



Morphology. The human skeleton consists of two parts, 

 skeleton and the appendicular skeleton. 



The axial skeleton embraces the bones of the head, the 

 spine, the ribs, the hyoid bone, and the breast bone. In the 

 spine are included not only the vertebrae of the cervical, 

 thoracic, and lumbar regions, but likewise the sacrum and 

 coccyx. 



The appendicular skeleton embraces the bones of the limbs, 

 or extremities, including the shoulder-girdle, formed by the 

 scapula and clavicle, and the pelvic 

 girdle, formed by the innominate bone 

 (Fig. 226). 



Function. The upper extrem- 

 ity in man is an organ of prehension. 

 As such, mobility is its chief charac- 

 teristic. To permit of this mobility 

 the bones and joints are many, and 

 the latter are comparatively loose; 

 the muscles, also, are both numerous 

 and complex. Hence it is that slight 

 injuries are frequently followed by 

 considerable disturbance of function. 

 They are readily produced and with 

 difficulty repaired, either by nature 

 or by art. Orthopaedic surgery has 

 done much for the disabilities and de- 

 formities of the lower extremities, but 

 comparatively little for those of the 

 upper. An artificial leg in many cases 

 satisfactorily substitutes the natural 

 one, but an artificial arm is compara- 

 tively useless. 



The hand is the essential part 

 of the upper extremity, and the rest 

 of the limb is subsidiary. If the forearm were lack- 

 ing and the hand were attached to the end of the 

 humerus it would still be a very useful appendage, 

 far more so than the stump which is left after the hand 

 has been amputated. 



The extremities proper are joined to the trunk by 

 what are called girdles. The upper extremity is 

 attached through the medium of the shoulder-girdle 

 and the lower extremity by the pelvic girdle. The 

 interposition of these girdles adds to the mobility of 

 the extremities, and as the upper extremity is more 

 mobile than the lower we find the shoulder-girdle com- 

 posed of two bones instead of one as in the pelvic 

 girdle ; also, as the lower extremity bears the weight 

 of the body it requires strength in addition to mobility, 

 hence we find that it is joined to the trunk by a single 

 big strong bone, the innominate, instead of by two 

 comparatively slight, narrow bones like the clavicle 

 and scapula which form the shoulder-girdle. 



The extremities are termed appendicular because 

 the 7 e ^P 1 ? appendages to the essential part, 

 and those of the upper and lower ex- which is the head and trunk; a person can live with- 



tremities constituting the appendicu- . 



lar skeleton. out extremities. 



