SCAPULAR VESSELS. 359 



directly back ; for as one tends to raise, and the other to depress the acro- 

 mion, the bone will be moved in a direction between the two forces. By 

 their united action the muscles help to fix the scapula. 



The OMO-HYOID MUSCLE consists of two fleshy bellies, anterior and 

 posterior, which are united by an intervening tendon. Only the posterior 

 half is now seen. 



The muscle arises from the upper border of the scapula behind the 

 notch, and from the ligament converting the notch into a foramen. The 

 fibres form a thin, riband-like muscle, which is directed forwards across 

 the lower part of the neck, and ends anteriorly in a tendon beneath the 

 sterno-mastoideus (p. 72). The fleshy belly of the muscle is placed partly 

 beneath the trapezius ; and is partly superficial in the posterior triangular 

 space of the neck, where it lies above the clavicle and the subclavian 

 artery. It crosses the suprascapular vessels and nerve, and the brachial 

 plexus near the scapula. 



Action. For the supposed use of the posterior belly of the omo-hyoideus, 

 see page 72. 



The suprascapular artery, a branch of the subclavian (p. 78), is directed 

 outwards across the lower part of the neck to the dorsum of the scapula. 

 The vessel courses behind the clavicle with the suprascapular nerve, but 

 beneath the trapezius and omo-hyoid muscles to the supraspinal fossa. 

 Before entering the fossa it furnishes a small branch (supra-acromial) to 

 the upper surface of the acromion. 



The suprascapular nerve, an offset of the brachial plexus (p. 79), is 

 inclined backwards to the superior border of the scapula. It passes through 

 the notch in the upper costa of the bone, and terminates beneath the supra- 

 spinatus in the muscles of the dorsum of the scapula (p. 248). 



The transverse cervical artery, also a branch of the subclavian (p. 78), 

 has the same direction as the suprascapular, towards the upper part of the 

 scapula, but it is higher than the clavicle. Crossing the upper part of the 

 space in which the subclavian artery lies, it passes beneath the trapezius, 

 and divides into the two following branches superficial cervical and pos- 

 terior scapular : 



a. The superficial cervical branch is distributed chiefly to the under 

 surface of the trapezius, though it furnishes offsets to the levator anguli 

 scapulas and the cervical glands. 



b. The posterior scapular branch crosses beneath the elevator of the 

 angle of the scapula, and turns along the base of the scapula beneath the 

 rhomboid muscles. If the rhomboid muscles are divided, the artery will 

 be seen to furnish branches to them ; and to give small anastomotic twigs 

 to both surfaces of the scapula. This branch arises very frequently from 

 the third part of the subclavian trunk. 



The supra-scapular and transverse cervical veins have the same course 

 and branches as the arteries above described ; they open into the external 

 jugular, near its junction with the subclavian vein. 



Nerve to the rhomboid muscles. This slender nerve of the brachial plexus 

 (p. 79) courses beneath the elevator of the angle of the scapula, and is 

 distributed to the rhomboidei on the under surface. Before its termination 

 it supplies one or two twigs to the elevator of the scapula. 



* THIRD LAYER (fig. 117). In this stratum are the following muscles : 

 the serratus posticus superior and inferior, with the splenius. 



* Dissection. By reflecting the rhomboidei muscles towards the spinous 



