96 TOPOGRAPHIC AND APPLIED ANATOMY. 



PLATE 6. 



A posterior view of the opened head, neck, and trunk of a man. The greater portion of the brain has been 

 removed; the spinal cord and spinal nerves as well as the viscera and diaphragm may be seen in situ. From a 

 Leipzig model from nature (His). 



ratus magnus muscle, which it supplies. This artery varies in size and is often absent. The 

 mammary branches of this vessel have been previously mentioned. The long thoracic nerve, 

 for the serratus magnus muscle, does not run with the artery but somewhat posteriorly [that is, 

 in the angle made by the inner and posterior walls of the axilla. ED.], covered by the latissi- 

 mus dorsi muscle. 



3. The subscapular artery, the largest branch of the axillary, arises to the outer side of the 

 long thoracic artery at the axillary border of the scapula. It is covered by the latissimus dorsi 

 muscle and is not endangered by operative procedures in the axilla until they penetrate beneath 

 the margin of this muscle. One of the terminal branches, the thoracicodor sails, runs onward 

 in the continuation of the main trunk, as the largest artery of the lateral thoracic wall, between 

 the serratus magnus and latissimus dorsi (and teres major) to supply these muscles. The other 

 terminal branch, the dorsalis scapula, passes posteriorly through the triangular space (see page 

 76) to reach the dorsal surface of the scapula. 



The arteries running upon the internal surface of the thoracic wall are known as the inter- 

 costal arteries. These vessels originate from three sources: 



1. From the costocervical trunk of the subclavian (see page 70) is given off the small supe- 

 rior intercostal artery, which descends beneath the pleura in front of the necks of the first two 

 ribs and supplies the two upper intercostal spaces. 



2. The thoracic aorta gives off nine intercostal branches, for the third to the eleventh inter- 

 costal spaces inclusive, and a tenth branch for the lower margin of the twelfth rib. These vessels 

 arise from the dorsal surface of the thoracic aorta. As the aorta lies to the left side of the ver- 

 tebral column, the right intercostal arteries are longer than the left ones. The vessels of the 

 right side pass over the vertebra toward the right and are situated behind the esophagus, the 

 vena azygos major, and the right sympathetic nerve. The shorter vessels of the left side are 

 behind the vena azygos minor and the left sympathetic nerve. At the necks of the ribs the 

 arteries give off posterior branches which run backward and divide into a spinal branch, entering 

 the vertebral canal through the intervertebral foramen and supplying the spinal cord, and a 

 muscular and cutaneous branch. The continuation of the artery or the anterior branch, usually 

 designated simply as the intercostal artery, runs in the intercostal groove along the inferior border of 

 the rib, at first being covered only by the pleura, and then passes anteriorly between the internal 

 and external intercostal muscles; it sends a small branch to the upper border of the rib 

 below, gives off cutaneous branches which appear externally (with mammary branches, see page 

 94), and anastomoses with the anterior intercostal branches of the internal mammary artery. 



3. The anterior intercostal branches of the internal mammary artery, which pass backward 

 and anastomose with the aortic intercostals. These vessels run in the upper six intercostal 

 spaces, the lower six being supplied with corresponding branches by the musculophrenic artery. 



The intimate relation of the intercostal arteries with the intercostal grooves, which furnish 

 them with an external bony protection, explains the following statements: (i) Injuries of the 



