1096 THE EESPIEATOEY SYSTEM. 



cartilage. The middle lobe of the right lung is triangular or wedge-shaped in 

 outline. 



Variations. Variations in the pulmonary fissures are fairly common. Thus, it sometimes 

 happens that the middle lobe of the right lung is imperfectly cut off from the lobus superior. 

 Supernumerary fissures also are not infrequent, and in this way the left lung may be cut into 

 three lobes, and the right lung into four or even more lobes. The occurrence of the lobus azygos 

 in the right lung is a variation of some interest, seeing that such a lobe is constant in certain 

 mammals. It is a small accessory lobe, pyramidal in form, which makes its appearance on the 

 lower part of the mediastinal surface of the right lung. In certain cases the vena azygos 

 is enclosed within a fold of pleura, and is sunk so deeply in the pulmonary substance of the right 

 lung that it marks off a small accessory lobe. 



RADIX PULMONIS. 



The term root of the lung is applied to a number of structures which enter 

 and leave the lung at the hilurn on its mediastinal surface. They are held 

 together by an investment of pleura, and constitute a pedicle which attaches 

 the lung to the mediastinal wall of the pleural cavity. The phrenic nerve passes 

 downwards a short distance ventral to the pulmonary root, whilst the vagus nerve 

 breaks up into the dorsal or posterior pulmonary plexus on its dorsal aspect under 

 cover of the investing pleura. The delicate ventral or anterior pulmonary plexus 

 is placed ventral to the root of the lung under cover of the pleura, whilst from the 

 inferior border of the root of the lung the ligamentum pulmonale extends towards 

 the diaphragm. These relations are common to the pulmonary root on both sides 

 of the body, but there are others which are peculiar to each side. On the right 

 side the vena cava superior lies ventral to the pulmonary root, whilst the vena 

 azygos arches over its upper border. On the left side the aorta arches above the 

 root of the lung, whilst the descending thoracic aorta passes dorsal to it. 



Constituent Parts of the Pulmonary Root. The large structures which enter 

 into the -formation of the pulmonary root are (1) the two pulmonary veins, (2) 

 the pulmonary artery, (3) the bronchus. But in addition to these there are 

 one or more small bronchial arteries and veins, the pulmonary nerves and the 

 pulmonary lymph vessels, and some bronchial glands. 



The pulmonary nerves come from the vagus nerve and also from the sympathetic system. 

 They enter the lung and follow the air-tubes through the organ. The bronchial arteries are 

 small vessels which carry blood for the supply of the lung-tissue.. They arise from the aorta or 

 from an intercostal artery, and vary in number from one to three for each lung. In the root of 

 the lung they lie on the dorsal aspect of the bronchus, and they follow the air-tubes through 

 the organ. Part of the blood conveyed to the lung by the bronchial arteries is returned by the 

 pulmonary veins ; the remainder is returned by special bronchial veins which open on the right 

 side into the vena azygos, and on the left side into the vena hemiazygos. 



The lymph-vessels of the lungs are numerous and well developed, and are divided into two 

 groups, superficial and deep. 



The superficial lymph-vessels form a network on the surface of the lung and eventually 

 terminate by four or five vessels in the broncho-pulmonary glands of the hilum. It is usually 

 stated that the superficial lymph vessels communicate freely with the deep. This, however, is 

 denied by Miller, who maintains that anastomoses between the two systems of vessels are very 

 rare. A specimen of secondary carcinoma of the lung in the Pathology Museum of the University 

 of Melbourne shows a direct continuation of the disease through the lung-substance from the 

 surface to the tubes by way of the lymph vessels, and would thus tend to disprove Miller's 

 assertion. 



The deep lymph-vessels are subdivided into bronchial accompanying the bronchi and vascular 

 accompanying the blood-vessels. Both systems communicate freely together, and at the level of 

 the hilum terminate in the broncho-pulmonary glands. 



The pulmonary or broncho-pulmonary lymph-glands, found at the hilum, are usually numen 

 and variable in size. They are situated either just outside the lung or within the lung-substance 

 itself. 



From these broncho-pulmonary glands the lymph-flow is continued onward from the lung, 

 partly directly into the thoracic duct, and partly by a more circuitous route as follows : 



From the broncho-pulmonary lymph-glands vessels pass on to the tracheo-bronchial glai 

 situated at the angles produced by the bifurcation of the trachea into the two bronchi. Of these 

 glands there are, therefore, three groups, an inferior and right and left superior. From thesf 

 glands the lymph- flow is continued upwards through the tracheal lymph -glands lying on eitl 

 .side of the trachea into the deep cervical lymph-glands, and thence into the thdracic duct. 



The bronchus in the root of the lung lies dorsal to the great pulmonary vessels 



