648 THE ARTERIES. 



and immediately descends along the inner face of that bone to the sternum, 

 remaining covered by the pleura. It then bends backwards, passes under the 

 triangularis sterni muscle and above the sternal cartilages, which it crosses near 

 the chondro-sternal articulations, and reaches the base of the xiphoid cartilage, 

 where it ends in two branches — one abdominal, the other thoracic, and which 

 have been named the anterior abdominal and asternal arteries. 



In its course, the internal thoracic artery sends off collateral branches, which 

 may be distinguished into superior, inferior, and external. The superior are 

 always very slender, and proceed to the pericardium and mediastinum. The 

 inferior (Fig. 375, 11) are very large, and traverse the intercostal spaces to enter 

 the pectoral muscles, where they meet the ramifications of the external thoracic 

 artery. The external branches (Fig. 375, 10) follow the intercostal spaces ; 

 each generally divides into two branches, which finally anastomose by inoscula- 

 tion with the terminal divisions of the first seven intercostal arteries. 



Terminal branches of the interned thoracic artery. 1. Anterior abdominal 

 artery. — This vessel separates from the asternal artery at an acute angle, and 

 passes directly backward to escape from the chest by coureing beneath the xiphoid 

 cartilage ; it then places itself on the superior face of the rectus abdominis, 

 which it enters, after detaching lateral branches to the abdominal walls, and 

 anastomoses by its terminal ramifications with the posterior abdominal artery. 



2. Asternal artery. — This vessel glides within the cartilaginous circle formed 

 by the false ribs, in crossing the digitations of the transversalis alxlominis, and 

 terminates at the thirteenth intercostal space, in which it ascends to anastomose 

 with the corresponding intercostal artery. It supplies in its track intercostal 

 branches, which comport themselves like the analogous branches of the internal 

 thoracic artery ; fine diaphragmatic arterioles : and abdominal divisions, which 

 particularly ramify in the transversahs abdominis. 



5. External, Inferior Thoracic, or External Mammary Artery 

 (Fig. 375, 12). 



Principally distributed to the deep pectoral muscles, this artery commences 

 at an acute angle in front of, but close to, the preceding, turns the anterior 

 border of the first rib, and then passes back against the internal face of the deep 

 and superficial pectoral muscles, in which are extended its collateral and terminal 

 divisions. It gives off a fine branch which accompanies the spur vein, and 

 ramifies in the panniculus carnosus. 



This artery sometimes rises from the supra-sternal vessel ; its volume is 

 subject to great variations, and we have seen it entirely absent. 



6. Inferior Cervical or Trachelo-muscular Artery (Fig. 375, 8, 8'). 



Arising opposite the two preceding vessels, sometimes near the external, and 

 at other times near the internal mammary arteries, this vessel is at first situated 

 in the gulf between the jugulars, within the anterior superficial pectoral muscle, 

 and above the glands at the entrance to the chest ; it divides after a short course 

 into two branches, which separate at a very acute angle. One of these, the 

 superior {ascending cervical of Man), rises between the mastoido-humeralis and 

 subscapulo-hyoideus muscles, to which it is distributed, as well as to the glands 

 at the point of the shoulder, and the anterior superficial pectoral and angularis 

 scapulae muscles. 



