THE AXILLA m 635 



gives branches to the lower part of the pericardium, and others which run back- 

 ward to the Diaphragm and downward to the Abdominal muscles. 



The superior epigastric (a. epigastrica si/perior) continues in the original direc- 

 tion of the internal mammary; it descends through the cellular interval between 

 the costal and sternal attachments of the Diaphragm, and enters the sheath of the 

 Rectus abdominis muscle, at first lying behind the muscle, and then perforating 

 it and supplying it, and anastomosing with the deep epigastric artery from the 

 external iliac. Some branches perforate the sheath of the Rectus and supply the 

 muscles of the abdomen and the integument, and a small branch, which passes 

 inward upon the side of the ensiform appendix, anastomoses in front of that 

 cartilage with the superior epigastric artery of the opposite side. It also gives 

 some twigs to the Diaphragm, while from the artery of the right side small branches 

 extend into the falciform ligament of the liver and anastomose with the hepatic 

 artery. 



Applied Anatomy. The course of the internal mammary artery may be defined by drawing 

 a line across the six upper intercostal spaces half an inch from and parallel with the sternum. 

 The position of the vessel must be remembered, as it is liable to be wounded in stabs of the 

 thoracic wall. It is most easily reached by a transverse incision in the second intercostal space. 



The superior intercostal (trundis costocervicalis) (Figs. 447 and 465) arises from 

 the upper and back part of the subclavian artery, behind the Scalenus anticus mus- 

 cle on the right side and to the inner side of that muscle on the left side. Passing 

 backward, it gives off the deep cervical branch, and then descends behind the 

 pleura in front of the necks of the first two ribs, and anastomoses with the first 

 aortic intercostal. As it crosses the neck of the first rib it lies to the inner side 

 of the anterior division of the first thoracic nerve and to the outer side of the first 

 thoracic ganglion of the sympathetic. 



In the first intercostal space it gives off a branch which is distributed in a manner 

 similar to the distribution of the aortic intercostals. The branch for the second 

 intercostal space usually joins with one from the highest aortic intercostal. Each 

 intercostal gives off a branch to the posterior spinal muscles, and a small branch 

 which passes through the corresponding intervertebral foramen to the spinal cord 

 and its membranes. 



The deep cervical branch (a. cervicalis profundd) arises, in most cases, from 

 the superior intercostal, and is analogous to the posterior branch of an aortic 

 intercostal artery; occasionally it arises as a separate branch from the subclavian 

 artery. Passing backward, above the eighth cervical nerve and between the 

 transverse process of the seventh cervical vertebra and the first rib, it runs up the 

 back part of the neck, between the Complexus and Semispinalis colli muscles, 

 as high as the axis vertebra, supplying these and adjacent muscles, and anasto- 

 mosing with the deep branch of the arteria princeps cervicis of the occipital, 

 and with branches which pass outward from the vertebral. It gives off a special 

 branch which enters the vertebral canal through the intervertebral foramen 

 between the seventh cervical and first thoracic vertebrae. 



THE AXILLA. 



The axilla is a pyramidal space, situated between the upper and lateral part 

 of the. thorax and the inner side of the arm. 



Boundaries. Its apex, which is directed upward toward the root of the neck, 

 corresponds to the interval between the first rib, the upper edge of the scapula, 

 and the clavicle, through which the axillary vessels, the brachial plexus of nerves, 

 and the long thoracic nerve pass. This interval is the cervicoaxillary passage. 



