A Reference handbook of the medical sciences embracing the entire range of scientific and practical medicine and allied science . e to form the inferior cava,communicate with the cardinal veins. The inferior ex-tremities of the cardinal veins are persistent as the inter-nal iliac veins; above the iliac veins the cardinal veinsare obliterated ina considerablepart of theircourse; their up-per portions thenbecome continu-ous with two newvessels, iht poster-ior rertebral veinsof Rathke, whichreceive the lumbara n (1 intercostaltwigs, Asdevelopmentproceeds, the di-rection of theducts of Cuvier isal
A Reference handbook of the medical sciences embracing the entire range of scientific and practical medicine and allied science . e to form the inferior cava,communicate with the cardinal veins. The inferior ex-tremities of the cardinal veins are persistent as the inter-nal iliac veins; above the iliac veins the cardinal veinsare obliterated ina considerablepart of theircourse; their up-per portions thenbecome continu-ous with two newvessels, iht poster-ior rertebral veinsof Rathke, whichreceive the lumbara n (1 intercostaltwigs, Asdevelopmentproceeds, the di-rection of theducts of Cuvier isaltered by the de-scent of the heartto the thoracic re-gion, and then itbecomes continu-ous with that ofthe primitive jug-u 1 a r V e i n s. Acoinmuuicatingbranch makes itsappearance be-tween the twojugulars, directed obliquely downward from left to riglit; further down inthe dorsal region, between the posterioi veitebral veins,another communicating branch is developed. The communicating branch between the jugulars isconverted into the left innominate vein (see Fig. 4996).The jjortiou of the primitive jugular below the commu-. Fifi. —Double Vena Cava seen from theFront, with Small Transverse InnominateVeins. CR. Quain.) 201 REFERENCE HANDBOOK OF THE MEDICAL SCIENCES. nicating vein, together with the right duct of Cuvier,forms the superior vena cava, while the cardinal veinopening into it («;, Fig. 4994) is the extremity of tliegreat azygos vein. On the left side, the portion of theprimitive jugular placed heloiv the commimicatiugbranch, and the cardinal and posterior vertebral veins,together with the cross branch between the two posteriorvertebral veins, are converted into the left superior in-tercostal and left siiperior and inferior azygos left duct of Cuvier is obliterated, except at its lowerend, which always remains pervious as the coronarysinus. Traces oftliis vein are recognized in the adult asa fibrous band or a small vein (see Fig. 4996, ^
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