THORACIC CAVITY 63 



however, not uncommon, and the number may be increased 

 to five, three on the right one from each lobe of the right 

 lung and two on the left. On the contrary the number may 

 be reduced to two one on each side. 



The pulmonary veins commence in the capillary plexuses 

 between the walls of the alveoli; they accompany the 

 bronchi, lying, as a rule, along their anterior faces, and they 

 gradually unite together until on each side a terminal venous 

 stem is formed in each lobe. The stems from the upper and 

 middle lobes on the right side fuse together to form the upper 

 right pulmonary vein. On the left side the stem from the upper 

 of the two lobes forms the upper left pulmonary vein. On 

 both sides the stem from the lower lobe is the lower left 

 pulmonary vein. 



The pulmonary veins carry arterial (oxygenated) blood from 

 the lungs to the left atrium of the heart, whence it passes 

 to the left ventricle and is then distributed to all the tissues 

 of the body. 



Vasa Lymphatica Pulmonum et Lymphoglandulae Pul- 

 monales et Bronchiales. The lymph vessels of the lungs 

 cannot be displayed in an ordinary " part," but the bronchial 

 lymph glands, on account of their blackness and the dense 

 fibrous tissue which binds them to the adjacent bronchi and 

 blood-vessels, are disagreeably obvious, for they considerably 

 increase the difficulties of the dissector who is attempting to 

 clean the constituent parts of the root of the lung and the 

 bronchi. 



The lymph vessels of the lung convey lymph from the 

 substance of the lung to the pulmonary lymph glands, which 

 lie in the substance of the lung in the angles between the 

 branches of the bronchial tubes. Having passed through the 

 pulmonary lymph glands the lymph is carried onwards, by 

 their efferent vessels, to the broncho-pulmonary lymph glands, 

 which lie in the hilum of the corresponding lung in the 

 angles between the stem and the highest branches of the 

 bronchus. The broncho-pulmonary lymph glands also receive 

 lymph directly from the visceral pleura. From the broncho- 

 pulmonary lymph glands the lymph passes to the tracheo- 

 bronchial lymph glands, which lie in the angle between the 

 bronchus and the trachea on the lateral side; and to the 

 inter-tracheo-bronchial lymph glands, which are placed in the 

 angle between the two bronchi below the trachea. The latter 



