io84 A MANUAL OF ANATOMY 



border of the sterno-cleido-mastoid and joins it towards the lower 

 part of the neck. Further, it communicates with its fellow of the 

 opposite side by a transverse branch which crosses in front of the 

 trachea, and lies in Burns's space. 



The anterior jugular veins are usually asymmetrical, one or other 

 being of small size. Occasionally there is only one vein, which is 

 mesially placed, and, under these circumstances, it divides into two 

 vessels interiorly. The anterior jugular vein is destitute of valves. 



The external jugular vein commences close behind the angle of 

 the inferior maxilla in the substance of the parotid gland, where it 

 is formed by the union between the posterior division of the temporo- 

 maxillary vein and the posterior auricular vein. Having emerged 

 from the parotid gland it descends almost vertically to a point above 

 the centre of the clavicle. In its course the vessel crosses the sterno- 

 cleido-mastoid muscle, lying superficial to its sheath, and beneath 

 the superficial fascia containing the fibres of the platysma myoides. 

 At this level the main part of the superficial cervical nerve courses 

 forwards beneath the vein, and offsets of the nerve pass over it. 

 Having crossed the sterno-cleido-mastoid muscle, the vein descends 

 not far from its posterior border, where it lies in the roof of the sub- 

 clavian or supraclavicular triangle, over the third part of the sub- 

 clavian artery. Up to this point the vessel is superficial to the 

 deep cervical fascia, but it now pierces that fascia and opens into 

 the subclavian vein. 



The course of the external jugular vein is indicated by a line 

 drawn from a point close behind the angle of the inferior maxilla 

 to a point above the centre of the clavicle. Its tributaries are as 

 follows : (i) posterior jugular, which joins it about the middle of 

 the neck ; (2) transverse cervical ; (3) suprascapular ; and (4) anterior 

 jugular, the latter three joining it not far from its termination. It 

 also communicates with the anterior jugular vein by one or more 

 branches. The vessel is provided with valves, both at its termina- 

 tion and about ij inches above this point, and the transverse 

 cervical and suprascapular veins are also furnished with valves, 

 where they open into the external jugular vein, or near their 

 orifices. 



The external jugular vein is sometimes very small, or even absent ; 

 and it may communicate with the cephalic vein by a vessel which 

 passes over the clavicle. 



Development. — The external jugular vein is usually regarded as being 

 developed from the primitive jugular vein; but according to some authorities 

 the primitive jugular vein gives rise to the internal jugular vein, the external 

 jugular being of later development. 



. The posterior jugular vein represents the most external occipital 

 vein, and is formed by tributaries which issue from the outer part 

 of the occipital plexus, reinforced by veins from the superficial 

 structures at the back of the neck. Having usually received the 

 mastoid emissary vein, it passes downwards and forwards, and 

 joins the external jugular vein about the middle of the neck. 



