182 CIRCULATORY SYSTEM. 



spinalis and its membranes. Under the utias, the vertebral 

 trunk receives a large vessel of communication from the internal 

 carotid : its further description, however, must be suspended 

 until we come to trace the vessels of the brain. 



4. The internal pectoral artery, less in volume than 

 the vertebral, leaves the trunk below, opposite to the origin of 

 that vessel above, protected by the first rib, along the posterior 

 and inner margin of which it descends in a perpendicular direc- 

 tion towards the sternum. Leaving the lower extremity of the 

 rib, it makes a broad sweep downward and backward, and 

 descends upon the internal surface of the second bone of the 

 sternum : it afterwards diverges gradually from its fellow, tra- 

 verses the ends of the cartilages of the posterior true ribs, and, 

 having crossed that of the last, splits into two divisions. One of 

 these ascends upon the internal part of the chest along the border 

 of the seventh true cartilage ; thence it crosses the false cartilages, 

 detaching slender ramifications to them which anastomose with 

 some of the posterior intercostals, and makes its way towards the 

 flank, and disperses its ultimate branches among the muscles 

 there, souie of which reach far enough to communicate with the 

 ramifications of the circumflex artery of the ileum. The other 

 division (generally considered as the continuation of the trunk, 

 being rather the larger one) pierces the sheath of the rectus, and 

 makes it appearance upon the upper surface of that muscle, over 

 which it ramifies extensively, sending branches out again to anas- 

 tomose with the epigastric. Exclusively of these divisions, the 

 trunk detaches muscular branches along the first rib, inwardly 

 anterior mediastinal vessels, larger brandies to the muscles of the 

 sternum, and inferior mediastinal ; and also thymic twigs. 



5. The external pectoral artery, comparatively 

 small and unimportant, comes off also from the under part of the 

 trunk, makes a turn downward in front of the sternum, and dis- 

 tributes its ramifications among the pectoral muscles. This ar- 

 tery in some subjects is derived from the internal pectoral. 



6. The inferior cervical artery, longer and larger 

 than the afore-described vessel, arises from the common trunk 

 opposite to or in company with it, and makes its exit from the 

 chest below the vertebral artery, and then bends outward. At 

 the bottom of the neck it divides into several branches : these run 

 principally to the contiguous muscles, though some few ramify 

 with the adipose substance in the neighbourhood, and others are 

 destined to the absorbent glands hereabouts. 



7. The seventh and last branch, and largest (if we except the 

 carotids on the right side, and the continuation of the main trunk 

 on the left), is the 



