276 



THE DEVELOPMENT OF THE VASCULAR SYSTEM 



•corporated into the inferior vena cava. The lumoar veins develop from the same 

 prevertebral plexus that gives rise to the caudal segment of the inferior vena cava. 



Begg (Anat. Rec, vol. 10, 1916), on the contrary, finds that in the rat, where the meso- 

 nephroi are diminutive, the posterior cardinal veins are not incorporated into the mesonephroi 

 to disappear with that organ, but the right posterior cardinal persists as the segment of the 

 inferior vena cava below the subcardinal contribution. 



V. linguo-facialiS' 



Dorsal subclavian vein, 



Vena ulnaris 

 prima 



V. lingtw-facialis 

 Ant. cardinal vein 



■Com. cardinal vein 



Dorsal subclavian, 

 vein 



V . ulnaris prima 



V. thoraco-epigaslrica Fast, cardinalvein 



V. thoraco- Ventral sub- 

 ep2gastrica daman vein 



V. cephalica 



D 



V. linguo-facialis V. jugularis 

 externa 



V. cephalica 



V. card. ant. 



V. card. com. 

 V. card post. 



V. jugidaris interna 



V. linguo-facialis 

 V.jug. anterior 



anonyma 

 dextra 



V. anonyms 



sinistra 

 V. mammaria 



int. 



V. brackialis 



Fig. 285. — Four reconstructions of the veins of the human right arm (after F. T. Lewis). X about IS. 

 A, 10 mm. embryo; B, 11.5 mm. embryo; C, 16 mm. embryo; D, 22.8 mm. embryo. 



The Veins of the Extremities. — The primitive capillary plexus of the upper and lower ■ 

 limb buds gives rise to a border vein (Figs. 285 and 321), which courses about the periphery of 

 the flattened limb buds (Hochstetter). In the upper extremity, the ulnar portion of the 

 border vein persists, forming at different points the subclavian, axillary, brachial, and basilic 

 veins. The border vein at first opens into the dorsal wall of the posterior cardinal vein (em- 

 bryos of 10 mm.), but, as the heart shifts its position caudalward, it finally drains by a ventral 

 connection into the anterior cardinal or internal jugular vein (Lewis). The cephalic vein 



