THE SCAPULA 203 



along a line at right angles to and passing through the center of the glenoid cavity, 

 forming a considerable angle, called the subscapular angle; this gives greater 

 strength to the body of the bone by its arched form, while the summit of the 

 arch serves to support the spine and acromion. 



The dorsal surface (Fig. 203) is arched from above downward, and is subdivided 

 into two unequal parts by the spine; the portion above the spine is called the 

 supraspinatous fossa, and that below it the infraspinatous fossa. 



The supraspinatous fossa, the smaller of the two, is concave, smooth, and broader 

 at its vertebral than at its humeral end; its medial two-thirds give origin to the 

 Supraspinatus. 



The infraspinatous fossa is much larger than the preceding; toward its vertebral 

 margin a shallow concavity is seen at its upper part; its center presents a promi- 

 nent convexity, while near the axillary border is a deep groove which runs from 

 the upper toward the lower part. The medial two-thirds of the fossa give origin 

 to the Infraspinatus; the lateral third is covered by this muscle. 



The dorsal surface is marked near the axillary border by an elevated ridge, 

 which runs from the lower part of the glenoid cavity, downward and backward 

 to the vertebral border, about 2.5 cm. above the inferior angle. The ridge serves 

 for the attachment of a fibrous septum, which separates the Infraspinatus from 

 the Teres major and Teres minor. The surface between the ridge and the axillary 

 border is narrow in the upper two-thirds of its extent, and is crossed near its 

 center by a groove for the passage of the scapular circumflex vessels; it affords 

 attachment to the Teres minor. Its lower third presents a broader, somewhat 

 triangular surface, which gives origin to the Teres major, and over which the Latis- 

 simus dorsi glides; frequently the latter muscle takes origin by a few fibers from 

 this part. The broad and narrow portions above alluded to are separated by an 

 oblique line, which runs from the axillary border, downward and backward, to 

 meet the elevated ridge: to it is attached a fibrous septum which separates the 

 Teres muscles from each other. 



The Spine (spina scapulae). The spine is a prominent plate of bone, which 

 crosses obliquely the medial four-fifths of the dorsal surface of the scapula at its 

 upper part, and separates the supra- from the infraspinatous fossa. It begins 

 at the vertical border by a smooth, triangular area over which the tendon of inser- 

 tion of the lower part of the Trapezius glides, and, gradually becoming more ele- 

 vated, ends in the acromion, which overhangs the shoulder- joint. The spine is 

 triangular, and flattened from above downward, its apex being directed toward 

 the vertebral border. It presents two surfaces and three borders. Its superior 

 surface is concave; it assits in forming the supraspinatous fossa, and gives origin 

 to part of the Supraspinatus. Its inferior surface forms part of the infraspinatous 

 fossa, gives origin to a portion of the Infraspinatus, and presents near its center 

 the orifice of a nutrient canal. Of the three borders, the anterior is attached to the 

 dorsal surface of the bone; the posterior, or crest of the spine, is broad, and presents 

 two lips and an intervening rough interval. The Trapezius is attached to the supe- 

 rior lip, and a rough tubercle is generally seen on that portion of the spine which 

 receives the tendon of insertion of the lower part of this muscle. The Deltoideus 

 is attached to the whole length of the inferior lip. The interval between the lips 

 is subcutaneous and partly covered by the tendinous fibers of these muscles. The 

 lateral border, or base, the shortest of the three, is slightly concave; its edge, thick 

 and round, is continuous above with the under surface of the acromion, below 

 with the neck of the scapula. It forms the medial boundary of the great scapular 

 notch, which serves to connect the supra- and infraspinatous fossae. 



The Acromion. The acromion forms the summit of the shoulder, and is a large, 

 somewhat triangular or oblong process, flattened from behind forward, projecting 

 at first lateralward, and then curving forward and upward, so as to overhang the 



