52 



Pleura. 



A.ctV.V. 



ma TO mar. /-nt 



388, Horizontal Section of the Thorax, showing the 

 relative Position of the Viscera, and the Reflections 



of the Pleurae. 



The parenchyma of the lung is composed of lobules, Lobull s. Insulac 

 pulmonalcs, which are quite distinct from each other. Each lobule is com- 

 posed of one of the ramifications of the bronchial tube and its terminal 

 air -cells, and of the ramifications of the pulmonary and bronchial vessels, 

 lymphatics and nerves. The walls of each lobular bronchial tube are 

 closely covered by numerous saccular dilatations, the air-cells, Cdlulae 

 pidmonales. The air-cells are surrounded by the capillary network, placed 

 between the pulmonary artery and vein ; the artery conveys the venous 

 blood to the lungs, the vein returns the purefied blood to the heart. 



In purely anatomical relation with the thoracic viscera are: 



The thyroid gland, Glandula thyreoidea; it is situated at the 

 upper part of the trachea, and consists of two lateral lobes, Cornua lateralia, 

 connected together by a narrow transverse portion, the isthmus ; occasionally 

 a third lobe, Cornu medium., arises from the isthmus. The glandular sub- 

 stance consists of round vesicles, which are closed cavities. 



The t h y m u s g 1 a n d is developed only in the foetus and up to 

 the second year of life, when it ceases to grow and gradually dwindles, 

 until at puberty it has almost disappeared. It lies partly in the thorax 

 and partly in the lower region of the neck, and is composed of two 

 lateral lobes, which become elongated inferiorly into two lateral cornua. 

 Its structure is analogous to the lymphatic glands. 



