248 THE SKELETON. 



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 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 Humerus. 



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

 sents for examination a shaft and two extremities. 



The Upper Extremity is the largest part of the bone ; it presents a rounded 

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

 eminences, the greater and lesser tuberosities (Fig. 197). 



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 

 of the Supraspinatus ; the middle one, to the Infraspinatus ; the lowest facet and 

 the 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. 



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

 is situated in 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 

 muscle. The tuberosities are separated from one another by a deep groove, the 

 bicipital 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 

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

 the bone. It is deep and narrow at the commencement, and becomes shallow and 

 a little broader as it descends. Its borders are called, respectively, the external 

 and internal bicipital ridges; to the former of which the name pectoral ridge is, 

 also, often applied. In the recent state this groove contains a prolongation of 

 the synovial membrane of the shoulder-joint, and its floor receives that portion 

 of the tendon of insertion of the Latissimus dorsi muscle which is reflected into 

 it from the internal bicipital ridge. 



The Shaft of the humerus is almost cylindrical in the upper half of its extent, 

 prismatic and flattened below, and presents three borders and three surfaces for 

 examination. 



The anterior border runs from the front of the great tuberosity above to the 



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. 



