142 MUSCLE TISSUE 



There are three important openings in the dia- 

 phragm, and several smaller ones. The esophageal 

 opening transmits the esophagus and vagi nerves, the 

 esophagus continues as the stomach below the dia- 

 phragm; the aortic opening transmits the abdominal 

 aorta, vena azygos major, and thoracic duct; it is the 

 most posterior one; the opening for the inferior vena 

 cava is the most anterior and transmits the large vein 

 which carries the venous blood to the right side of 

 the heart. The splanchnic nerves and the azygos 

 minor veins pierce the diaphragm near the crura. The 

 upper surface of the diaphragm is covered by peri- 

 cardium in the centre, pleurae on the lateral surfaces, 

 and the under surface is covered by peritoneum. 



Actions. It is the chief muscle of respiration; 

 thus when a deep breath is taken the diaphragm can 

 be felt to extend downward making pressure on the 

 abdominal organs, and at the same time increases 

 the vertical diameter of the thoracic cavity, allowing 

 the lungs to fill more readily with air. The diaphragm 

 also contracts in all expulsive acts, as sneezing, laugh- 

 ing, crying, coughing, and in the act of defecation, 

 urination, and expulsion of the fetus during delivery, 

 it assists the abdominal muscle to raise the intra- 

 abdominal pressure. The action of the diaphragm can 

 be seen in patients under ether, when the upper por- 

 tion of the abdomen will demonstrate the gradual 

 and steady ascent and descent of the diaphragm 

 under forced or abdominal breathing. 



The Fasciae and Muscles of the Abdomen 



The fascia of the abdomen is divided into a super- 

 ficial and deep portion. The superficial fascia is 

 continuous above with the fascia of the thorax and 

 back, below with that of the thigh. Its lower fourth 

 on the abdomen divides into a superficial layer 



