484 



DEVELOPMENT OF THE VEINS. 



the heart. Each is formed by the union of a superior and an inferior vein, named 

 the primitive jugular and the cardinal. 



The primitive jugular vein receives the blood from the cranial cavity by channels 

 in front of the ear, which are subsequently obliterated ; in the greater part of its 

 extent it becomes the external j ugular vein ; and near its lower end it receives small 

 branches, which grow to be the internal jugular and subclavian veins. The cardinal 

 veins are the primitive vessels which return the blood from the Wolffian bodies, the 

 vertebral column, and the parietes of the trunk. The inferior vena cava is a vessel of 

 later development, which opens into the trunk of the umbilical and omphalo-mesenteric 

 veins, above the venae hepaticae revehentes. The iliac veins, which unite to form the 

 inferior vena cava, communicate with the cardinal veins. The inferior extremities of 

 the cardinal veins are persistent as the internal iliac veins. Above the iliac veins, the 



Fig. 329. Fig. 329. DIAGRAMS ILLUSTRATING 



THE DEVELOPMENT OP THE GREAT 



VEINS (after Kolliker). 



A, plan of the principal veins of the 

 foetus of about four weeks, or soon after 

 the first formation of the vessels of the 

 liver and the vena cava inferior. 



B, veins of the liver at a somewhat 

 earlier period. 



C, principal veins of the foetus at the 

 time of the first establishment of the 

 placental circulation. 



D, veins of the liver at the same 

 period. 



dc, the right and left ducts of Cuvier ; 

 ca, the right and left cardinal veins ; 

 .;', j, the jugular veins ; s, the subclavian 

 veins ; az, the azygos vein ; w, the um- 

 bilical or left umbilical vein ; u' in B, 

 the temporary right umbilical vein ; o, 

 the omphalo-mesenteric vein ; e/, the 

 right omphalo-mesenteric vein ; m, the 

 mesenteric veins ; p, the portal vein ; 

 p', p', the vense advehentes ; I, the duc- 

 tus venosus ; I', I', the hepatic veins ; 

 ci t vena cava inferior ; il, the division 

 of the vena cava inferior into common 

 iliac veins ; cr, the external iliac or 

 crural veins ; h, the hypogastric or in- 

 ternal iliac veins, in the line of continua- 

 tion of the primitive cardinal veins. 



In C, li, in dotted lines, the trans- 

 verse branch of communication between 

 the jugular veins which forms the left 

 innominate vein ; ri, the right innomi- 

 nate vein ; ca', the remains of the left 

 cardinal vein by which the superior 

 intercostal veins fall into the left in- 

 nominate vein ; above p, the obliquely 

 crossing vein by which the hemiazygos 

 joins the azygos vein. 



cardinal veins are obliterated in a considerable part of their course ; their upper 

 portions then become continuous with two new vessels, the posterior vertebral veins of 

 Rathke, which receive the lumbar and intercostal twigs. 



As development proceeds, the direction of the ducts of Cuvier is altered by the 

 descent of the heart from the cervical into the thoracic region, and becomes con- 

 tinuous with that of the primitive jugular veins. A communicating branch makes its 

 appearance, directed transversely from the junction of the left subclavian and jugular 

 veins, downwards, and across the middle line to the right jugular; and further down 



