BASE OF THE NECK. 55 



much more convex than its clavicular, which is nearly flat, 

 and corresponds to a concavity in the sternum, so that the 

 articulation in reality is between the sternum and the flbro- 

 cartilage, and not between the sternum and clavicle. 



The inter-articular cartilage divides the joint into two 

 separate parts, each provided with a separate synovial 

 membrane. 



BASE OF THE NECK. 



At the root of the neck, the region exposed behind the 

 articulation above described, will exhibit the great venous 

 branches which return the blood from the head and upper 

 extremity. 



The internal jugular vein descends the neck on the outer 

 side of the carotid artery, and enters the subclavian vein, 

 which is the continuation of the axillary vein ; the internal 

 jugular vein at this point is provided with two valves. 



The SUBCLAVIAN VEIN lies in front of the artery of that 

 name, and the union of Jthis with the preceding vein forms 

 the VENA INNOMINATA. The vena innominata is further 

 reinforced by the vertebral vein, which descends at the side 

 of the vertebral artery through the foramina of the trans- 

 verse processes of the cervical vertebrae, and by the infe- 

 rior thyroid veins, coming from the thyroid body and its 

 neighborhood. The two venae innominatae unite to form 

 the SUPERIOR YENA CAVA, and, owing to the destination 

 of that vessel to the right auricle, the vena innominata of 

 the left side is longer than that of the right, and its 

 direction more nearly transverse ; it lies upon the three 

 primary branches of the aorta, and upon the upper part of 

 the arch itself. The thoracic duct enters the left vena in- 

 nominata at its commencement ; the precise point may be 

 demonstrated by inflating the duct in the thorax with a 

 blow-pipe. The ductus lymphaticus dexter, which is the 

 termination of the lymphatic vessels of the right side of 

 the head and neck, right arm, and right side of the thorax, 

 enters the right vena innominata near its commencement. 

 The orifices of both these lymphatic ducts are provided 

 with sigmoid valves to prevent admission of blood. 



Between the subclavian vein and artery may be traced 

 the pneumogastric and phrenic nerves. 



The pneumogastric nerve has been already seen higher in 

 the neck, lying between the carotid artery and internal 

 jugular vein (p. 52); its lower part is now to be observed. 



