The scapula (shoulder blade) is a flat bone lying against the cranial part of the lateral thoracic wall.
The scapula presents:
- A costal surface (medial surface), facing the ribs that is hollowed by the shallow subscapular fossa occupied by the origin of the subscapular muscle. At the proximal part of the costal surface is a closely defined area called facies serrata for the origin of the serratus ventralis.
- A lateral surface is divided by the spine of the scapula into a smaller cranial supraspinous fossa (for origin of the supraspinous muscle) and a larger caudal infraspinous fossa (for origin of infraspinous muscle). The spine of the scapula extends from the dorsal border to the ventral angle, increasing in height dorsoventrally. The spine of the scapula ends with the acromion, a well-defined eminence, located close to the ventral angle in carnivores and ruminants but remaining distal in pigs and horses. The acromion extends ventrally in carnivores (hamate process) and extends caudally in cats (suprahamate process). The rabbits possess the both processes of acromion (hamate and suprahamate).
- A dorsal border facing the vertebral column. On it, is inserted the scapular cartilage (small in carnivores)
- A caudal border facing the tricipital region, marked by several rides for the attachment of the triceps muscle.
- A cranial border facing the neck of the animal. It presents the scapular notch where the suprascapular nerve lies, at the level of the neck of the scapula and dorsal to the supraglenoidal tubercle.
- A caudal angle joining the dorsal and caudal borders
- A cranial angle joining the dorsal and cranial borders
- A ventral angle bearing the glenoid cavity and separated from the proximal part of the scapula by the neck of the scapula.
The glenoid cavity, for the articulation with head of humerus, is located at the ventral angle of scapula. In horses, there is a craniomedial notch in the border of the glenoid cavity called the glenoid notch.
Cranially to the glenoid cavity is a large prominence, called the supraglenoid tubercle, for origin of the muscles of forearm. The coracoid process is a medial process on supraglenoid tubercle for origin of coracobrachial muscle; it remains small in domestic animals.
The infraglenoid tubercle is a small prominence at the caudal bordel dorsal to the ventral angle, for the origin of brachial triceps (carnivores and horses) and/or articularis humeri muscle (horses, cats and pigs).