SYSTEMIC VEINS. 



17 



outer ones. These run forward along the costal cartilages with the internal mammary 

 artery between the two of each lateral pair. The common trunk formed by the union 

 is very short. 



Each innominate divides into three trunks, the 

 vertebral, common jugular, and subclavian. The 

 vertebral goes to the head throu^gh the vertebral 

 canal. The common jugular is very short and is 

 formed by the union of an external and internal 

 jugular. The external lies laterally along the 

 neck. It is formed at the base of the skull by the 

 union of veins from the exterior of the head and 

 lower jaw. A short distance back of its anterior 

 end it is joined by a vein running forward from 

 the dorsal aspect of the shoulder and neck. 

 About half way down two smaller ones unite 

 with it that come from the dorsal surface of the 

 neck. Near its lower end, finally, a large branch 

 curves over the anterior aspect of the shoulder 

 from the dorsal surface of the same and unites 

 with it just in front of the shoulder. The mus- 

 cles of the neck and shoulder are hence abun- 

 dantly supplied with both arteries and veins; the 

 veins of this region emptying into the external 

 jugular corresponding in size and numbers with 

 the branches of the thyroid axis. The internal 

 jugular is formed at the base of the skull by the 

 union of numerous branches from the exterior 

 and interior of the head. The most important 

 of these are : Two veins curving around the pos- 

 terior ends of the lower jaw from the muscles 

 laterad of this and from the posterior lateral 

 aspect of the head ; a vein from the interior of 

 the cranium which leaves the same by a small 

 foramen in the anterior part of the ear capsule 

 and which then goes backward and downward 

 along the lesser cornu of the hyoid and receives 

 a branch from the tongue; a vein from the base 

 ,of the head and the soft palate, and the main 

 trunk from the jugular foramen in the skull. 

 The internal jugular is much larger than the ex- 

 ternal. It receives no important additions along 

 the neck. 



The subclavian vein is formed by the union of 

 numerous veins from the fore limb. 



The inferior vena cava is formed at a variable 

 point either between or back of the kidneys by the union of the converging common 

 iliac veins. Each of these is formed farther back by the union of the external and 

 5974— PT 3 2 



Fig. 6.— Posterior venous system of left side. 

 v.c.p. vena cava posterior. 



c. il. common iliac vein. 

 ex. il. external iliac vein. 

 in. il. internal iliac vein. 

 fern, femoral vein. 



V. vein from plantar surface of hind flipper. 



c. s. median caudal and sacral vein. 



