462 



RESPIRATION 



passive process, depending mainly upon the elastic recoil of the parts 

 previously put on the stretch. The enlargement of the thoracic cavity 

 is accomplished in three directions, namely, along its vertical, transverse 

 and anteroposterior planes. 



The increase in the vertical diameter is effected with the help of the 

 diaphragm. This musculotendinous septum which forms the dividing 

 line between the thoracic and abdominal cavities, arises from the first 

 three or four lumbar vertebrae and adjoining fascia, from the borders 

 of the six lower ribs and from the ensiform cartilage. The individual 

 fibers strive radially toward a common center, keeping first in close 



Fig. 237. — Apparatus Arranged for Illustrating the Expansion of the Lung. 

 N, bell jar; B, rubber balloon; M, manometer. The rubber membrane closing the 

 bell jar is pulled down in imitation of the contraction of the diaphragm. This causes 

 the expansion of the balloon by a negative pressure resting upon its surface. The 

 upward movement of this membrane corresponds to expiration. The manometer is 

 connected with the space between the walls of the bell jar and the balloon (intra- 

 pleural space) and registers the changes in pressure. (Laulanie.) 



contact with the chest wall but later on turning rather abruptly to be 

 inserted into the edges of the tendinous central area of this septum. 

 The latter generally conforms to the outline of the body and appears 

 most frequently in two segments, a right and a left (Fig. 239). In 

 cross-section, therefore, the diaphragm presents a dome-shaped outline, 

 its convex surface being turned into the thoracic cavity. At the side, 

 only the smallest possible space separates its upper surface from the 

 wall of the chest so that its parietal pleura lies in absolute contact with 

 the parietal pleura lining the inner surface of the thorax. At a some- 

 what higher level, this capillary space, which is known as the '' com- 

 plementary'^ pleural cavity, soon widens out into the general cavity 

 of the thorax. 



