178 SPECIAL ANATOMY OF THE SKELETON 



process may be felt about an inch below the junction of the middle and outer thirds of the 

 clavicle. Here it is covered by the anterior border of the Deltoid and lies a little to the outer 

 side of a slight depression which corresponds to the interval between the Pectoralis major 

 and Deltoid muscles. When the arms are hanging by the side, the upper angle of the scapula 

 corresponds to the upper border of the second rib or the interval between the first and second 

 thoracic spines, the inferior angle to the upper border of the eighth rib or the interval between 

 the seventh and eighth thoracic spines. 



Applied Anatomy. Fractures of the body of the scapula are rare, owing to the mobility of 

 the bone, the thick layer of muscles by which it is encased on both surfaces, and the elasticity of 

 the ribs on which it rests. Fracture of the neck of the bone is also uncommon. The most fre- 

 quent course of a line of fracture of the neck is from the suprascapular notch to the infraglenoid 

 tubercle (surgical neck), and it derives its principal interest from its simulation to a subglenoid 

 dislocation of the humerus. The diagnosis can be made by noting the alteration in the position 

 of the coracoid process. A fracture of the neck external to, and not including, the coracoid 

 process (anatomical neck) is said to occur, but it is exceedingly doubtful whether such an 

 accident ever takes place. The acromion process is more frequently broken than any other 

 part of the bone, and there is sometimes, in young subjects, a separation of the epiphysis. It 

 is believed that many of the cases of supposed fracture of the acromion, with fibrous union, 

 which have been found on postmortem examination are really cases of imperfectly united 

 epiphysis. Sir Astley Cooper believed that most fractures of this bone are united by fibrous 

 tissue, and the cause of this mode of union is the difficulty that arises in keeping the fractured 

 ends in constant apposition. The coracoid process is occasionally broken off, either by direct 

 violence or perhaps, rarely, by muscular action. 



Tumors of various kinds grow from the scapula. Of the innocent form of tumors, probably 

 . the osteomata are the most common. When an osteoma grows from the anterior surface of the 

 scapula, as it sometimes does, it is of the compact variety, such as usually grows from mem- 

 brane-formed bones, as the bones of the skull. This would appear to afford evidence that this 

 portion of the bone is formed from membrane, and not, like the rest of the bone, from cartilage. 

 Sarcomatous tumors sometimes grow from the scapula, and may necessitate removal of the bone, 

 with or without amputation of the upper limb. Removal of the upper limb with the scapula and 

 the outer two-thirds of the clavicle is known as the' interscapulothoracic amputation. The scapula 

 may be partially resected or completely excised. There are several methods of complete excision. 

 The bone may be excised by a T-shaped incision, and, the flaps being reflected, the removal is 

 commenced from the vertebral border, so that the subscapular vessels which lie along the axillary 

 border are among the last structures divided, and can be at once secured. 



THE ARM. 



The arm is that portion of the upper extremity which is situated between the 

 shoulder and the elbow. Its skeleton consists of a single bone, the humerus. 



The Humerus, or Arm Bone (Figs. 141, 142). 



The humerus is the longest and largest bone of the upper extremity; it presents 

 for examination a shaft and two extremities. 



Upper or Proximal Extremity. The upper extremity presents a large, 

 rounded head, joined to the shaft by a constricted portion, called the neck, and 

 two other eminences, the greater and lesser tuberosities. 



The Head (caput humeri). The head, nearly hemispherical in form, 1 is directed 

 upward, inward, and slightly backward, and articulates with the glenoid cavity 

 of the scapula; its surface is smooth and coated with cartilage in the recent state. 

 The circumference of its articular surface is slightly constricted, and is termed 

 the anatomical neck, in contradistinction to the constriction which exists below the 

 tuberosities. The latter is called the surgical neck (collum chirurgicwn), as it is 

 often the seat of fracture. 



The anatomical neck (collum anatomicum) is obliquely directed, forming an 



1 Though the head is nearly hemispherical in form, its margin, as Sir G. Humphry has shown, is by no means 

 a true circle. Its greatest measurement is from the top of the bicipital groove in a direction downward, inward, 

 and backward. Hence, it follows that the greatest elevation of the arm can be obtained by rolling the articular 

 surface in this direction that is to say, obliquely upward, outward, and forward. 



