144 THE SKELETON. 



times, 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 post-mor- 

 tem examination are really cases of imperfectly united epiphysis. Sir Astley Cooper believed 

 that most fractures of this bone united by fibrous tissue, and the cause of this mode of union 

 was the difficulty there was in keeping the fractured ends in constant apposition. The coracoid 

 process is occasionally broken off, either from direct violence or perhaps, rarely, from muscular 

 action. 



Tumors of various kinds grow from the scapula. Of the innocent form of tumors prob- 

 ably the osteomata are the most common. When it grows from the venter of the scapula, as it 

 sometimes does, it is of the compact variety, such as usually grows from membrane-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. The bone may be excised by a T-shaped incision, and, 

 the flaps being reflected, the removal is commenced from the posterior or 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. 



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

 for examination a shaft and two extremities. 



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 (Fig. 97). 



The head, nearly hemispherical in form, 1 is directed upward, inward, and a 

 little 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 con- 

 tradistinction to the constriction which exists below the tuberosities. The latter 

 is called the surgical neck, from its often being the seat of fracture. It should be 

 remembered, however, that fracture of the anatomical neck does sometimes, though 

 rarely, occur. 



The anatomical neck is obliquely directed, forming an obtuse angle with the 

 shaft. It is more distinctly marked in the lower half of its circumference than in 

 the upper half, where it presents a narrow groove, separating the head from the 

 tuberosities. Its circumference affords attachment to the capsular ligament and 

 is perforated by numerous vascular foramina. 



The greater tuberosity is situated on the outer side of the head and lesser 

 tuberosity. Its upper surface is rounded and marked by three flat facets, sep- 

 arated by two slight ridges : the highest facet gives attachment to the tendon 

 ot the bupraspmatus ; the middle one, to the Infraspinatns ; the inferior facet and 



shaft of the bone below it, to the Teres minor. The outer surface of the great 

 tuberosity is convex, rough, and continuous with the outer side of the shaft. 



Ine lesser tuberosity is more prominent, although smaller than the greater : it 



is situated m front of the head, and is directed inward and forward. Its summit 



presents a prominent facet for the insertion of the tendon of the Subscapularis 



Ine tuberosities are separated from one another by a deep groove the 



biciptial groove, so called from its lodging the long tendon of the Biceps muscle, 



with which runs a branch of the anterior circumflex artery. It commences 



above between the two tuberosities, passes obliquely downward and a little 



mward, and terminates at the junction of the upper with the middle third of 



s deep and narrow at the commencement, and becomes shallow and 



broader as it descends. Its borders are called, respectively, the anterior 



