152 ANATOMY AND PHYSIOLOGY FOR NURSES 



center. The principal nerves concerned in respiration 

 are the phrenic and the pneumogastric or par vagum. 



Each pleural cavity is a closed sac, one occupying 

 the right, the other the left half of the thorax; they 

 are perfectly separate and do not communicate. They 

 meet in the middle line of the chest at the upper part only, 

 just behind the upper part of the gladiolus of the sternum. 

 Lower down a space (the mediastinum) is left between 



FIG. 73- Interior view of the diaphragm : 1-3, The three lobes of the 

 central tendon, surrounded by the fleshy fasciculi derived from the inferior 

 margin of the thorax ; 4, 5, the crura; 6, 7, the arcuate ligaments; 8, aortic 

 orifice; 9, esophageal orifice; 10, quadrate foramen ; n, psoas muscle; 12, 

 quadrate lumbar muscle. 



them, which contains all of the viscera of the thorax 

 excepting the lungs. 



The mediastinum is the space left in the median 

 portion of the chest by the non-approximation of the two 

 pleura; it extends from the sternum in front to the spine 

 behind. It is divided into an upper and a lower portion : 

 the upper is called the superior; the lower or inferior is 

 divided into three subdivisions, called respectively the 



