34 6 KESPIRATION. [CH. xxiv. 



lymphatic vessels which lead from these accompany the pul- 

 monary vessels towards the root of the lung. 2. Irregular anas- 

 tomosing spaces in the walls of the bronchi, y. Lymph-spaces 

 in the pulmonary pleura. The lymphatic vessels from all these 



Fig. 317. Capillary network of the pulmonary blood-vessels in the human lung, x 60. 



(KOlliker.) 



irregular sinuses pass in towards the root of the lung to reach the 

 bronchial glands. 



Nerves. The nerves of the lung are to be traced from the 

 anterior and posterior pulmonary plexuses, which are formed by 

 branches of the vagus and sympathetic. The nerves follow the 

 course of the vessels and bronchi, and in the walls of the latter 

 many small ganglia are situated. 



The Respiratory Mechanism. 



Respiration consists of the alternate expansion and contraction 

 of the thorax, by means of which air is drawn into or expelled 

 from the lungs. These acts are called Inspiration and Expiration 

 respectively. 



For the inspiration of air into the lungs it is evident that all 

 that is necessary is such a movement of the side-walls or floor of 

 the chest, or of both, that the capacity of the interior shall be 

 enlarged. By such increase of capacity there will be a diminution 

 of the pressure of the air in the lungs, and a fresh quantity will 

 enter through the larynx and trachea to equalise the pressure on 

 the inside and outside of the chest. 



For the expiration of air, on the other hand, it is also evident 



