THORAX OF THE FOETUS. 



529 



Fig. 



birth the quantity of fluid secreted from the thymus, gradu- 

 lly declining, as that of chylification becomes perfectly estab- 

 shed. j 



The arteries of this body are de- 

 rived from the thyroid branches of 

 the subclavians, from the internal 

 mammaries, and the vessels of the 

 pericardium and mediastinum. The 

 veins terminate mainly in the left 

 vena innominata. 



The nerves are very minute, and 

 are chiefly from the plexus about the 

 internal mammary artery which comes 

 from the superior thoracic ganglion of 

 the sympathetic. The lymphatics ter- 

 minate at the common junction of the 

 other vessels of the kind, at the union 

 of the internal jugular and subclavian 

 veins. Sir A. Cooper has injected 

 them but once in the human foetus. 

 In the calf he found two large lym- 

 phatic ducts, see fig. 131, which com- 

 mence at the upper extremities of the 

 lobes, and pass downwards to termi- 

 nate at the junction of the jugular and 

 subclavian of each side. These ves- 

 sels he considers the absorbent ducts 



of the glands the thymic ducts which carry the fluid from 



the reservoir of the thymus into the veins. 



The Heart, 



And the great arteries which proceed from it, have some very 

 interesting peculiarities in the foetus. 



* The course and termination of the " absorbent ducts " of the thymus of 

 the calf; from one of Sir Astley Cooper's preparations. 1. The two internal 

 jugular veins. 2. The superior vena cava. 3. The thoracic duct, dividing into 

 two branches, which re-unite previously to their termination in the root of the 

 left jugular vein. 4. The two thymic ducts ; that on the left side opens into 

 the thoracic duct, and that on the right into the root of the right jugular vein. 



45 



