The posterior surface (dorsal surface) 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 prominent 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 Latissimus 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.