LIGAMENTS OF STERNUM, ETC. Ill 



lower three or four costal cartilages, and is inserted by 

 fleshy dictations into the cartilages of the third, fourth, 

 fifth, and sixth ribs, and often into that of the second. 

 This muscle varies frequently in its extent and points of 

 attachment. 



The INTERNAL MAMMARY ARTERY, detached by this sec- 

 tion from its connection with the subclavian, descends upon 

 each side of, and about half an inch from the sternum ; it 

 gives off the anterior inter costals, which turn outward in the 

 upper five or six intercostal spaces to inosculate with the 

 aortic intercostals, and furnish the branches which perforate 

 the intercostal muscles, close to the sternum, to be dis- 

 tributed to the pectoralis major muscle and the integument 

 of the thorax. A small branch, the comes nervi phrenici, 

 given off as soon as the artery enters the chest, and which 

 descends to the diaphragm with the phrenic nerve, will have 

 been cut off and left behind. Some small twigs, called 

 mediastinal and pericardiac, will also be found. At the 

 interval between the sixth and seventh ribs, it gives off a 

 large branch called the musculo-phrenic, which winds along 

 the attachment of the diaphragm to the ribs, and supplies 

 the lower intercostal spaces. The termination of the inter- 

 nal mammary is sometimes called the superior epigastric 

 artery; it passes downward between the rectus muscle and 

 its sheath, and inosculates with the epigastric branch of 

 the external iliac. This artery occasionally gives off on 

 both sides, from near its origin, a good-sized branch, which 

 might be called an internal thoracic artery; it traverses 

 the ribs near their middle, to the fifth intercostal space, 

 where it becomes an intercostal artery. 



LIGAMENTS OF THE STERNUM, AND COSTAL CARTILAGES. 



The two bones of the sternum are connected by an in- 

 tervening fibro-cartilage. Upon the anterior and posterior 

 surfaces their union is strengthened by longitudinal fibres, 

 which blend with other similar fibres radiating from the 

 costal cartilages, and, in front, with the sternal tendinous 

 origins of the pectoral muscles. The anterior aspect of the 

 sternum is therefore rough and fibrous, while the posterior 

 is comparatively smooth. 



The cartilages of the ribs, received into the lateral fossa3 

 of the sternum, are each provided with a synovial mem- 

 brane, and held in place by radiating ligamentous fibres, 

 anteriorly and posteriorly, which blend with those of the 



