THE THORAX, 351 



branches (excepting the first), which pierce the overlying 

 muscles and supply the side of the body from the axilla to 

 the crest of the ilium. Each lateral cutaneous nerve 

 divides into an anterior and posterior branch in passing to 

 its distribution. In addition to this the lateral cutaneous 

 branch of the second nerve passes to supply the posterior 

 upper part of the arm, and is called the intercostohumeral 

 nerve. See page 280. 



The Diaphragm. Figs. 71, 75. 



Origin. From the posterior surface of the ensiform ap- 

 pendix, from the inner surface of the cartilages of the six 

 lower ribs, from the ligamentum arcuatum externum 

 and internum, and by two crura from the anterior surface 

 and intervertebral discs and anterior common ligament of 

 the first to the fourth lumbar vertebrae (on the right side), 

 and from the first to the second or third (on the left side). 



Insertion. Into the central tendon, which presents three 

 portions or leaves, two lateral and one central. 



Nerve Supply. The phrenics, bringing filaments from the 

 third, fourth, and fifth cervical nerves. These nerves pass 

 through the muscle and are distributed to its under surface. 



Action. To produce inspiration by lengthening the verti- 

 cal dimension of the thorax. To compress the viscera and 

 aid in all expulsive efforts, as defalcation, micturition, par- 

 turition, and vomiting. In vomiting the diaphragm con- 

 tracts to form a hard surface against which the stomach 

 is compressed by the action of the abdominal muscles. 



Openings Through the Diaphragm. 



Aortic opening lies immediately in front of the spine. It 

 gives passage to the aorta, vena azygos major, and thoracic 

 duct. 



The cesophageal opening lies in front of the aortic to the 



