The =external surface= or =dorsum= (Facies lateralis s. dorsalis) is divided into two fossæ by the =spine= (Spina scapulæ), which extends from the vertebral border to the neck of the bone, where it gradually subsides. The free edge of the spine is thick, rough, and in great part subcutaneous. A little above its middle is a variable prominence, the =tubercle= of the spine (Tuber spinæ), to which the trapezius muscle is attached. The =supraspinous fossa= (Fossa supraspinata) is situated in front of the spine, and the =infraspinous fossa= (Fossa infraspinata) behind it. The former is much the smaller of the two; it is smooth and is occupied by the supraspinatus muscle. The infraspinous fossa lodges the infraspinatus muscle; it is wide and smooth in its upper part, narrower below, where it is marked by several rough lines for the attachment of the teres minor muscle; near the neck is the nutrient foramen, and a little lower is a vascular groove. [Illustration: FIG. 41.—LEFT SCAPULA OF HORSE, EXTERNAL VIEW. (After Schmaltz, Atlas d. Anat. d. Pferdes.) ] The =costal surface= or =venter= (Facies costalis) is hollowed in its length by the =subscapular fossa= (Fossa subscapularis); this occupies nearly the whole of the lower part of the surface, but is pointed above and separates two rough triangular areas (Facies serrata), to which the serratus magnus is attached. In the lower third there is a vascular furrow with several branches. The =anterior= or =cervical border= (Margo cranialis) is convex and rough above, concave and smooth below. The =posterior= or =dorsal border= (Margo caudalis) is slightly concave. It is thick and rough in its upper third, thin in its middle, and thickens again below. The =superior= or =vertebral border= (Margo dorsalis s. basis) carries the =scapular cartilage= (Cartilago scapulæ). In the young subject the edge of the bone is thick, and is pitted by impressions into which the cartilage fits. The cartilage is the unossified part of the fœtal scapula. Its lower edge fits the depressions and elevations of the bone. It thins out toward the free edge, which is convex and lies alongside of the upper parts of the vertebral spines. In front it continues the line of the scapula, but behind it forms a rounded projection. The lower part of the cartilage undergoes more or less ossification, so that the vertebral border of the bone in old subjects is thin, irregular, and porous. [Illustration: FIG. 42.—LEFT SCAPULA OF HORSE, COSTAL SURFACE.—(After Schmaltz, Atlas d. Anat. d. Pferdes.) ] The =anterior= or =cervical angle= (Angulus cranialis) is at the junction of the anterior and vertebral borders and lies opposite to the second thoracic spine. It is relatively thin and is about a right angle. The =posterior= or =dorsal angle= (Angulus caudalis) is thick and rough; its position can be determined readily in the living animal.