730 HUMAN ANATOMY. 



toid muscle are divided just above their origin. The anterior jugular vein runs 

 behind the sternal head, and is to be avoided or tied. The thyroid plexus of veins 

 may appear in the wound, and should be tied or drawn out of the way. The 

 sterno-hyoid and sterno-thyroid muscles are divided close to the sternum. The deep 

 cervical fascia is divided in the line of the superficial wound. The common carotid 

 artery should be found, its sheath opened, and the vessel traced down to the innomi- 

 nate bifurcation. The internal jugular vein may be much engorged and should be 

 drawn outward. The innominate vein may protrude into the wound. Osteoplastic 

 resection of the manubrium (Bardenheuerj, or a median longitudinal division of that 

 bone (Woolsey) with retraction of the edges, will facilitate the exposure of the 

 vessel. The most important relations are to the outer side, — viz., the vagus, the 

 pleura, and the right innominate vein. The left common carotid and trachea lie to 

 the inner side. The needle should be passed from without inward. The ligature 

 should be placed as high as possible, to leave room between it and the aorta for the 

 formation of a satisfactory clot. It is well to ligate the common carotid and the 

 vertebral at the same time, to lessen the risk of secondary hemorrhage on the distal 

 side of the ligature. 



The collateral circulation is carried on from the proximal or cardiac side of the 

 ligature by {a) the first aortic intercostal ; {b) the upper aortic intercostals ; (f) the 

 inferior phrenic branch of the abdominal aorta (within the diaphragm); {d^ the 

 deep epigastric (within the rectus sheath) ; {e) the vertebrals and internal carotids 

 of the left side (within the cranium — circle of Willis) ; and {f) the branches of the 

 left external carotid ; anastomosing respectively with («) the superior intercostal of 

 the subclavian ; {b') the intercostals of the internal mammary and the thoracic 

 branches of the axillary ; (r) the musculo-phrenic branch of the internal mammary ; 

 (^ ) the superior epigastric branch of the internal mammary ; (<?) the vessels in the 

 right half of the circle of Willis ; and {f) the branches of the right external carotid, 

 all receiving their blood-supply from beyond — or to the distal side of — the ligature. 



THE COMMON CAROTID ARTERIES. 



The right common carotid artery arises from the innominate and the left one from 

 the arch of the aorta (Fig. 690). Both pass directly upward in the neck, along the 

 side of the trachea and larynx, and terminate opposite the upper border of the thyroid 

 cartilage by dividing into the external and internal carotid arteries, their course being 

 represented by a line drawn from a point midway between the angle of the jaw and 

 the mastoid process to the sterno-clavicular articulation. Throughout its course 

 neither of the common carotids gives of? any branches, and they consequently have 

 an almost uniform calibre, except towards their point of division, where they present 

 a dilatation frequently continued into the internal carotid and usually becoming more 

 marked with advancing age. 



Relations.^ — The left common carotid lies in the thoracic cavity during the 

 first part of its course, and in this respect differs from the right artery, whose origin 

 from the brachio-cephalic is at the level of the sterno-clavicular articulation. This 

 thoracic portion of the left common carotid is usually about 3 cm. ( i ^ in. ) in 

 length, and is crossed obliquely in front, near its root, by the left innominate 

 (brachio-cephalic) vein and by the cardiac branches of the pneumogastric nerve. It 

 is separated from the sternum and the origin of the sterno-thyroid muscle by some 

 fatty tissue which contains the remains of the thymus gland, and posteriorly it is in • 

 relation with the trachea below and higher up with the left recurrent laryngeal nerve. 

 Below, to its right side and a short distance away, is the innominate artery ; above 

 it is in close relation with the trachea, while to its left and somewhat posteriorly are 

 the left subclavian artery and the left pneumogastj^ic nerve. 



Throughout their cervical portions the relations of both arteries are iden- 

 tical. Each is enclosed within a tibrous sheath formed by the deep cervical fascia 

 (page 550), the sheath also containing the internal jugular vein and the pneumo- 

 gastric nerve, the vein lying lateral to the artery and the nerve between the two 

 vessels, but in a plane slightly posterior to them. Extending downward for a vari- 

 able distance upon the anterior surface of the sheath is the descending hypoglossal 



