630 Mu. c. H. o'donoghue on the 



(B) Adult Form. 

 {a) Anterior Vessels. 



The whole of the blood from the head is brought back to the 

 heart by the two common jugular veins. The distribution of the 

 veins in the head and their union to form the common jugulars 

 will be dealt with later. 



The Left Common Jugular Vein * (Y. jugularis sinister, Schlemm) 

 runs from the anterior end of the neck parallel with and close to 

 the left common carotid artery to the heart. It passes ventral to 

 the left systemic arch to the dorsal side of the left auricle, and it 

 runs along the dorso-lateral edge of this structure to the auriculo- 

 ventricular sulcus. Here it bends sharply to the right and runs 

 into a part of the sinus venosus somewhat sharply marked off 

 from the remainder. It receives : — 



i. In its anterior part a few small tributaries from the anterior 



end of the ffisophagus. 

 ii. The Coronary Veins (text-fig. 87), a series of small vessels 



which join it in its course along the auriculo-ventricular 



sulcus. 



The Right Common Jtigidar Vein * (V. jugularis dextra, 

 Schlemm) is similar in disposition to the left, but at the level of 

 the anterior end of the right auricle it receives a large tributary, 

 the azygos vein. After this it runs straight on and unites with 

 the post-caval vein to form the major part of the sinus venosus. 



I. The Azygos Vein (Y. azygos, Schlemm) is a short trunk 

 leading into the right common jugular vein from the union of the 

 anterior and posterior azygos veins. 



A. The Anterior Azygos Vein (Y. azygos anterior, Schlemm) lies 

 in front of the heart between the oesophagus and the 

 backbone, and extends from the beginning of the neck 

 back to the heart. It collects blood from the dorsal body- 

 wall along this region by means of a fairly regala,r series 

 of intercostal veins, all of which come off to the right of 

 the vertebral column. Just before it unites with the 

 posterior azygos vein it receives a branch from the 

 oesophagus. 



{a) The CEsophageal Vein is formed at the level of the front 

 end of the thyroid gland by the union of two branches. 

 One of these branches comes from the anterior dorsal 

 part of the oesophagus, and the other from the posterior 

 dorsal part. Their common stem runs almost straight 

 to the right, ventral to the vertebral artery and dorsal 

 to the right common jugular vein, and opens into the 

 anterior azj'gos vein. 



* It is to be noted that the pi'oximal parts of these two veins aie homologous 

 with the precaval veins of Lacertilia. As, however, there is no representative of the 

 subclavian veins to mark the beginning of the precaval portion, it is convenient to 

 applj' the one name to the whole vessel. 



