216 CIRCULATORY SYSTEM. 



receives also, as it crosses over the ribs, other small veins, and 

 these likewise contribute to its volume. 



The Pectoral Vein 

 Answers in course and distribution to the pectoral artery. 

 It originates in branches from the abdominal parietes, continues 

 to receive laterally accessory vessels in its passage, and ascends 

 along the inner and posterior border of the first rib, in front of 

 the artery, to arrive at the under part of the vena cava anterior. 



The Dorso-Cervical Fein 

 Consists of two divisions ramifying along with the dorsal 

 and posterior cervical arteries, and returning blood from the 

 muscles they supply. It also receives the anterior intercostal 

 vein, the companion of the artery so named, which is the com- 

 mon trunk of the veins corresponding to the second, third, 

 fourth, and fifth intercostal arteries. 



27ie hiferior Cervical Vein 



Is the vessel or vessels descending along the inferior part of 

 the neck in company with the inferior cervical artery. Its 

 principal branches are muscular; though some come from the 

 skin and absorbent glands in the vicinity. 



The Vena Azi/gos, 

 The last and only single branch of the vena cava anterior, in 

 whose supero-posterior part it ends, just as the trunk opens 

 into the auricle. It arises, as far backward as the loins, by 

 some small straggling veins ; and takes its course across the 

 bodies of the dorsal vertebrae, on the right side of the posterior 

 aorta, growing somewhat larger as it advances towards its termi- 

 nation, where it forms a remarkable curvature downward, to 

 reach the trunk of the cava. It receives at its origin many veins 

 from the neighbouring muscles, those of the loins more particu- 

 larly; but its destined office is to conduct the blood from the 

 posterior intercostal veins — from twelve to thirteen of them on the 

 right side, from eight to nine only on the left, in consequence of 

 its being placed inconveniently for the reception of more of the 

 latter : had the vena cava posterior been raised alongside of the 

 posterior aorta, a vena azygos would not have been required ; it 

 may be said, therefore, to supply the place of that vessel along 

 the spine. 



Posterior Vena Cava. 

 This is the correspondent venous trunk to the posterior aorta — 



