THE HUMERUS. 253 



and Flexor carpi ulnaris ; to the external condyloid ridge, the Supinator longus 

 and Extensor carpi radialis longior ; to the external condyle, the common tendon 

 of the Extensor carpi radialis brevior, Extensor comnmnis 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, 

 an 1 the only parts of this bone which are strictly subcutaneous are small portions of the 

 internal and external comlyles. 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 

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

 aeromion 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 rece lt-s from under the fintrer. The lesser tuberosity. directed forward and inward, is to be 

 felt to the inner side of the greater tuberosity. just below the acromio-clavicular 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 

 boil" are to be felt. Of these the internal is the more prominent, but the ridge passing upward 

 from it. the internal condyloid 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 -les. From it is to be felt a strong bony ridge running up the outer border of the shaft of 

 the hone. This is the external condyloid ridge; it is concave forward, and corresponds with 

 the curved direction of the lower extremity of the humerus. 



Surgical 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 

 epiphysis. Hence, in cases of amputation of the arm in young subjects the humerus continues 

 to urow considerably, and the end of the bone which immediately after the operation was cpv- 

 eivl with a thick cushion of soft tissue, begins to project, thinning the soft parts and rendering 

 the stump conical. This may necessitate the removal of a couple of inches or so of the bone, 

 and even after this operation a recurrence of the conical stump may take place. 



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

 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 action 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. I have seen the accident happen from throwing a stone, and in 

 an apparently healthy adult from cutting a piece of hard cake tobacco" on a table. In this 

 latter case there was no disease of the bone that could be discovered. Fractures of the upper 

 end may take place through the anatomical neck, through the surgical neck, or separation of the 

 greater tuberosity may o x-ur. Fracture of the anatomical neck is a very rare accident; in fact. 

 it i- doubted by some whether it ever occurs. These fractures are usually considered to be 

 intraeapsular. but they are probably partly within and partly without the capsule, as the lower 

 part of the capsule is inserted some little distance below the anatomical neck, while the upper 

 part is attached to it. They may be impacted or non-impacted. 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. But occasionally a very remarkable alteration in position takes place ; the upper 

 fragment turns on its own axis, so that the cartilaginous surface of the head rests against the 

 upper end of the lower fragment. When the fractured end is entirely separated from all its 

 surroundings, its vascular supply must be entirely cut off, and one would" expect it, theoretically, 

 to necrose. But this must be exceedingly rare, for Gurlt was unable to find a single authenti- 

 cated case recorded. Separation of the upper epiphysis of the humerus sometimes occurs in the 

 young subject, and is marked by a characteristic 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 some 

 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 con- 

 nection with these fractures are ( 1 ) that the musculo-spiral 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 '!) the frequency of non-union. 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 probably 

 to be due to the difficulty that there is in fixing the shoulder-joint and the upper fragment, and 

 possibly also the elbow-joint and lower fragment also. Other causes which have been assigned 

 for the non-union are: (1) that in attempting 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 consequence of the rigidity of the elbow, in attempting 



