GREAT VESSELS AND NERVES OF NECK 309 



major) _and the scalenus anterior. Between its posterior 

 surface and the scalenus anterior are the ascending cervical 

 artery, the phrenic nerve, and, crossing superficial to the latter, 

 the transverse cervical and the transverse scapular arteries. 

 On the left side the terminal part of the thoracic duct also 

 crosses the phrenic nerve posterior to the internal jugular vein. 

 At the medial border of the scalenus anterior the thyreo- 

 cervical artery is posterior to it, and at a lower level, the 

 first part of the subclavian artery and the dome of the pleura. 



The right vein is usually the larger of the two ; and as 

 they approach the root of the neck both veins incline slightly 

 to the right, with the result that, on the right side, the lower 

 part of the vein is separated from the common carotid artery 

 by a small triangular interval bounded below by the subclavian 

 artery, whilst on the left side the vein overlaps the anterior 

 aspect of the common carotid artery. 



Tributaries. Immediately below its commencement the 

 internal jugular vein is joined by the inferior petrosal sinus, 

 and then, successively, by offsets from the pharyngeal plexus, 

 by the lingual vein, the common facial vein, the superior and 

 middle thyreoid veins. In some cases it is joined near its 

 upper end by a vena comes which runs with the occipital 

 artery; and, occasionally, near its lower end, it receives the 

 lymph trunks which usually open into the commencement 

 of the innominate vein. 



Dissection. Slit open the lower part of the vein and examine the valve 

 which lies close to its extremity. It consists of two or three semilunar 

 flaps which prevent regurgitation of blood from the innominate vein into 

 the internal jugular. 



Nervi Glosso-pharyngeus, Vagus, Accessoriiis. After 

 the removal of the. brain these nerves were seen leaving 

 the cranial cavity through the middle compartment of the 

 jugular foramen in the interval between the commencement 

 of the internal jugular vein postero-laterally and the inferior 

 petrosal sinus antero-medially (p. 215, and Fig. 125, p. 310). 

 The dissector should again examine the interior of the cranial 

 cavity and refresh his memory as to the manner in which 

 they enter the foramen. The glosso-pharyngeal occupies 

 the most anterior position, and it is cut off from the others 

 by a separate tube-like sheath of dura mater. The accessory 

 is placed posterior to the vagus, and both are included 

 within the same sheath of dura mater. They therefore 

 ii 20 b 



