REGION OF THE CAROTID ARTERIES. 91 



pulled inwards, the sheath being reached (upon which 

 are branches of the loop of the descendens and communi- 

 cans noni nerves), it is to be opened, and the needle 

 passed from without inwards. The inferior thyroid 

 artery and sympathetic and recurrent laryngeal nerves 

 lie immediately behind the vessel in this part of its 

 course. It must be borne in mind that, on the right 

 side of the neck, at its lower part, the internal jugular 

 vein diverges from the artery; but on the left approaches 

 it, and sometimes crosses it, owing to the formation of 

 the innominate veins. As before mentioned, advantage 

 may be taken of the natural interspace between the two 

 heads of origin of the sterno-mastoid to place a ligature 

 on this portion of the vessel, but it is very difficult for 

 the reason just stated (Sedillot). Another method of 

 reaching it is to expose and divide the sternal attach- 

 ment of the sterno-mastoid, thereby obtaining greater 

 room and corresponding safety (Malgaigne). 



Collateral circulation after Ligature of the Common Caro- 

 tid. Supposing the vessel to be normal that is to say, 

 that it gives off no branch before the usual bifurcation, 

 the collateral circulation is very free, and is re-established 

 by vessels both without and within the cranium ; thus, 

 the current of blood being arrested in the carotid, the 

 subclavian of the same side becomes dilated, the work 

 outside the skull is thrown upon the inferior thyroid 

 branch of the thyroid axis, the superior thyroid branch 

 of the external carotid, the profunda cervicis of the 

 superior intercostal, and the princeps cervicis of the oc^ 

 cipital ; the vertebral doing the work of the internal car- 

 otid, within the skull. 



Ligature of the External Carotid Artery. An incision 

 is to be made similar to, that for tying the common car? 



