184 SPECIAL ANATOMY OF THE SKELETON 



alls longior; to the external condyle, the common tendon of the Extensor carpi radialis brevior, 

 Extensor comrnunis digitorum, Extensor minimi digiti, Extensor carpi ulnaris, and Supinator 

 [brevis]; to the back of the external condyle, the Anconeus. 



Surface Form. The humerus is almost entirely clothed by the muscles which surround it, 

 and the only parts of this bone which are strictly subcutaneous are small portions of the inter- 

 nal and external condyles. In addition to these, the tuberosities and a part of the head of the 

 bone can be felt under the skin and muscles by which they are covered. Of these, the greater 

 tuberosity forms the most prominent bony point of the shoulder, extending beyond the acromion 

 process and covered by the Deltoid muscle. It influences materially the surface form of the 

 shoulder. It is best felt while the arm is lying loosely by the side; if the arm be raised, it recedes 

 from under the finger. The lesser tuberosity, directed forward and inward, is to be felt to the 

 inner side of the greater tuberosity, just below the acromioclavicular joint. Between the two 

 tuberosities lies the bicipital groove. This can be defined by placing the finger and making 

 firm pressure just internal to the greater tuberosity; then, by rotating the humerus, the groove 

 will be felt to pass under the finger as the bone is rotated. With the arm abducted from the 

 side, by pressing deeply in the axilla the lower part of the head of the bone is to be felt. On 

 each side of the elbow-joint, and just above it, the internal and external condyles of the bone 

 may be felt. Of these, the internal is the more prominent, but the ridge passing upward from 

 it, the internal supracondylar ridge, is much less marked than the external, and, as a rule, is 

 not to be felt. Occasionally, however, we find along this border the hook-shaped process men- 

 tioned above. The external condyle is most plainly to be seen during semiflexion of the fore- 

 arm, and its position is indicated by a depression between the attachment of the adjacent mus- 

 cles. From it is to be felt a strong bony ridge running up the outer border of the shaft of the 

 bone. This is the external supracondylar ridge; it is concave forward, and corresponds with 

 the curved direction of the lower extremity of the humerus. 



Applied Anatomy. There are several points of surgical interest connected with the humerus. 

 First, as regards its development. The upper end, though the first to ossify, is the last to 

 join the shaft, and the length of the bone is mainly due to growth from this upper epiphy.sis. 

 Hence, in cases of amputation of the arm in young subjects the humerus continues to grow con- 

 siderably, and the end of the bone, which immediately after the operation was covered with a 

 thick cushion of soft tissue, begins to project, thinning the soft parts and rendering the stump 

 conical. This may necessitate another operation, which consists in the removal of a couple of 

 inches or so of the bone, and even after this operation a recurrence of the conical stump mav 

 take place. 



There are several points of surgical interest in connection with fractures. First, as regards 

 their causation, the bone may be broken by direct or indirect violence like the other long bones, 

 but, in addition to this, it is probably more frequently fractured by muscular acfion than any 

 other of this class of bone in the body. It is usually the shaft, just below the insertion of the 

 Deltoid, which is thus broken. Fractures of the upper end may take place through the 

 anatomical neck, through the surgical neck, or separation of the greater tuberosity may occur. 

 Fracture of the anatomical neck is a very rare accident; in fact, it is doubted by some whether it 

 ever occurs. These fractures are usually considered to be intracapsular, but they are probablv 

 partly within and partly without the capsule, as the lower part of the capsule is inserted some 

 little distance below 7 the anatomical neck, while the upper part is attached to it. They may be 

 impacted or nonimpacted. In most cases there is little or no displacement on account of the 

 capsule, in whole or in part, remaining attached to the lower fragment. Separation of the upper 

 epiphysis of the humerus sometimes occurs in the young subject, and is marked by a character- 

 istic deformity by which the lesion may be at once recognized. This consists in the presence 

 of an abrupt projection at the front of the joint a short distance below the coracoid process, 

 caused by the upper end of the lower fragment. In fractures of the shaft of the humerus the 

 lesion may take place at any point, but appears to be more common in the lower than in the 

 upper part of the bone. The points of interest in connection with these fractures are: (1) That 

 the musculospiral nerve may be injured as it lies in the groove on the bone, or may become 

 involved in the callus which is subsequently thrown out; and (2) the frequency of nonunion. 

 This is believed to be more common in the humerus than in any other bone, and various causes 

 have been assigned for it. It would seem most probablv to be due to the difficulty that there 

 is in fixing the shoulder-joint and the upper fragment, and possibly the elbow-joint and lower 

 fragment also. Other causes which have been assigned for the nonunion are: (1 ) That in attempt- 

 ing passive motion of the elbow-joint to overcome any rigidity which may exist, the movement 

 does not take place at the articulation, but at the seat of fracture; or that the patient, in con- 

 sequence of the rigidity of the elbow, in attempting to flex or extend the forearm moves the 

 fragment and not the joint. (2) The presence of small portions of muscle tissue between the 

 broken ends. (3) Want of support to the elbow, so that the weight of the arm tends to drag the 

 lower fragment away from the upper. An important distinction to make in fractures of the 

 lower end of the humerus is between those that involve the elbow-joint and those which do not; 

 the former are always serious, as they may lead to stiffness of the joint and impairment of the 



