SCAPULAR LIGAMENTS. 247 



Besides, there is a gliding movement of the acromion on the clavicle 

 in rotation of the scapula. For instance, when the acromion is depressed, 

 its articular surface moves from above down at the fore part of the joint, 

 and from below up at the back. When the acromion is elevated the sur- 

 face moves in exactly the opposite way. 



SCAPULAR LIGAMENTS. The special ligaments of the scapula are two 

 in number, anterior and posterior, and extend from one part of the bone 

 to another. 



The posterior ligament ( 4 ) is a narrow fasciculus of fibres stretching 

 across the notch in the upper costa of the scapula. By one end it is at- 

 tached to the base of the coracoid process, and by the other to the costa 

 behind the notch. It converts the notch into a foramen, through which 

 the suprascapular nerve passes. 



The anterior or coraco-acromial ligament ( 3 ) is triangular in form, and 

 extends transversely between the acromion and the coracoid process. Ex- 

 ternally it is inserted by its point or apex into the tip of the acromion ; 

 and internally, where it is much wider, it is attached to all the outer 

 border of the coracoid process, reaching backwards to the capsule of the 

 shoulder joint. The ligament consists usually of two thickened bands, 

 anterior and posterior, with a thin intervening part. It forms part of an 

 arch above the shoulder joint, which stops the ascent of the head of the 

 humerus. 



Dissection. To lay bare the supraspinatus muscle, the acromion pro- 

 cess is to be sawn through, and to be turned aside with the outer end of 

 the clavicle : but in the repetition of the dissection of the upper limb, the 

 bone may be left uncut for the purpose of seeing the use of the coraco- 

 acromial arch. A strong fascia covers the surface of the muscle ; this is 

 to be taken away after it has been observed. 



The SUPRASPINATUS MUSCLE (fig. 74, A ) has the same form as the 

 hollow of the bone it fills. It arises from the surface of the supra-spinal 

 fossa of the scapula, except from the cervical part ; from the upper side of 

 the spine of the bone ; and from the fascia covering the surface. Its fibres 

 end in a tendon, which crosses over the shoulder joint, and is inserted into 

 the upper impression of the great tuberosity of the humerus. 



The muscle is concealed by the trapezius and the acromion process ; 

 and it rests upon the scapula, the shoulder joint, and the suprascapular ves- 

 sels and nerve. Its tendon joins that of the infraspinatus at the attach- 

 ment to the humerus. 



Action. It comes into use with the deltoid in raising the limb, and 

 supporting the joint. 



Dissection (fig. 78). The vessels and nerves on the doroum of the 

 scapula can be traced by detaching from behind forwards the supra and 

 infraspinatus muscles, so as to leave a thin layer of the fleshy fibres with 

 the ramifying bloodvessels on the surface of the bone. In the supruspinal 

 fossa are the suprascapular vessels and nerve, which are to be followed 

 beneath the acromion to the infraspinal fossa ; and entering the infra- 

 spinal fossa, beneath the teres minor muscle, is the dorsal branch of the 

 subseapular artery. The anastomosis between those vessels should be pur- 

 sued in the fleshy fibres and cleaned. 



The suprascapular artery (a) is derived from the subclavian trunk, 

 and is one of the branches of the thyroid axis (p. 78). After a short 

 course in the neck it passes over the ligament at the superior costa, and 

 crossing beneath the supraspinatus muscle, ends in the infraspinal fossa, 



