THE COMMON CAROTID ARTERIES. 



731 



nerve, and overlapping it to a certain extent is the sterno-cleido-mastoid muscle 

 and, below, the sterno-hyoid and sterno-thyroid. At about the level of the cricoid 

 cartilage of the larynx the artery is crossed obliquely by the omo-hyoid muscle, and 

 higher up by the middle and superior thyroid, the lingual and sometimes the facial 

 veins, and the sterno-mastoid branch of the superior thyroid artery. 



Posteriorly the sheath rests upon the prevertebral fascia covering the longus colli 

 and the rectus capitis anticus major muscles, and is in relation with the ganglionated 

 cord of the sympathetic nervous system and its superior and middle cardiac 

 branches. Lower down, opposite the sixth cervical vertebra, the branches of the 



Fig. 690. 



Scalenus anticus 

 Thyroid axis. 



Right common carotid artery 



Right subclavian artery 



Internal mammary artery 



Left common carotid ar^. — 



Innominate artery — - 



Innominate veins 



Superior vena cava 



Left bronchus 

 Right pulmonary vein 



Right pulmonary artery 



Branch of right bronchus 



Right pulmonary vein 



Right auric ular appendage 

 Mesial surface of lung 



Right coronary artery 



Vertebral arteries 



Inferior thyroid arterj' 



Transverse cervical artery 



Suprascapular artery 



Thyroid axis 

 Clavicle 



Subclavian artery 

 Trachea 



Pericardium, upper limit 



Ligamentum arteriosum 

 Aorta, systemic 



Left pulmonary artery 

 Pulmonary aorta (artery) 



Pulmonary veins 



Right ventricle 

 {conus arteriosus) 



Mesial surface of lung 

 Left coronary artery 



Diaphragm 



:v 



Dissection showing aortic arch and its branches ; lungs have been pulled aside. 



inferior thyroid artery pass behind it. Medially are the trachea and the oesophagus, 

 together with the recurrent laryngeal nerve, the lobe of the thyroid gland, and, 

 above, the larynx and the pharynx. 



Variations. — The variations of the common carotid arteries have been sufficiently discussed 

 in coimection with the anomalies of the aortic arch (page 724). 



Practical Considerations. — Aneurism of the common carotid artery is not 

 very frequent. It most commonly occurs near the bifurcation {a) because of the 

 slight dilatation normally existing there ; {F) because there the vessel is more super- 



