42 TOPOGRAPHICAL ANATOMY OF THE 



costo-cervical artery (possibly in common with it), runs obliquely across 

 the oesophagus and the longus colli muscle, and leaves the chest between 

 the first and second ribs. Before leaving the thorax, it supplies a small 

 cranial mediastinal artery (a. mediastinalis cranialis) to the precardial 

 mediastinum, and the^irs^ intercostal artery (a. intercostalis prima). 



After leaving the thorax, the deep cervical artery divides into 

 transverse and ascending branches. The ramus transversus furnishes 

 vessels to the muscles in the neighbourhood of the junction of the neck 

 and thorax. The ramus ascendens passes up the neck in relation to 

 the ligamentum nuchae, and is examined during the dissection of the 

 neck. 



(3) A. vertehralis. — The vertebral artery passes in a cranial and 

 dorsal direction across the oesophagus to the thoracic entrance, where it 

 disappears between the longus colli and scalenus muscles. Its further 

 course belongs to the neck. 



(4) A. thoracica interna. — The internal thoracic artery leaves the 

 concave side of the left subclavian about the caudal border of the first 

 rib. Following the inner surface of the rib, it reaches the sternum 

 about the extremity of the second costal cartilage and there disappears 

 under the transverse thoracic muscle. Its subsequent course will be 

 followed later. 



(5) Truncus omocervicalis. — The omo-cervical ^ trunk arises about 

 the same level as the internal thoracic, but from the convex side of the 

 subclavian artery. Leaving the thorax at once, under the scalenus 

 muscle, it divides into ascending cervical and transverse scapular 

 arteries. 



(6) A. thoracica externa. — The external thoracic is the smallest 

 branch of the subclavian, and leaves the thorax by curving round the 

 sternal end of the first rib to pass backwards on the deep face of the 

 pectoral muscles. « 



A. BRACHIOCEPHALICA. — The brachio-cephalic artery is a short 

 vessel, of larger size than the left subclavian, placed between the trachea 

 and the cranial vena cava. It ends by dividing into the right sub- 

 clavian artery and the much smaller bicarotid trunk. As a rule there 

 is only one collateral branch, namely, a common vessel (costo-cervical 

 trunk) from which the right costo-cervical and deep cervical arteries 

 take origin. It will be noted that these vessels on the right side of the 

 body differ from those on the left in not having independent origins. 

 The common stem from which they spring crosses the right face of the 

 trachea and may extend so far as to come into contact with the longus 



' w/uos (omos) [Gr.], shoulder. Cervicalis [L.], pertaining to the neck (cervix). 



