8 CHARLES F. W. McCLUEE AND GEORGE S. HUNTINGTOST 



stetter's investigations, they are nevertheless lacking in de- 

 tails sufficient to explain all atypical conditions observed in 

 the adult mammal, especially in the cat. What we found to 

 be the case is that the posterior cardinal vein, as such, does 

 not, as has hitherto been supposed, enter into the formation 

 of the cava in the lumbar region of the cat. The dorsal limb 

 of the periureteric venous ring from which, according to 

 Hochstetter, the lumbar cava also is in part formed, does not 

 split off from the posterior cardinal, but belongs to a separate 

 and independent system of veins which we have designated 

 the supracardinal system of veins. 



In 1907, 2 we described the supracardinal system of veins 

 as follows : 



A bilateral and originally symmetrical venous channel develops 

 dorsomedial to the primitive postcardinal vein by longitudinal anas- 

 tomoses between somatic postcardinal tributaries. This secondary 

 vein channel forms what we have termed the supracardinal system 

 of veins. It extends from the level at which the posterior limb veins 

 open into the postcardinals to a point cephalad where it joins that 

 portion of the postcardinals which alone persists to form the anterior 

 end of the adult azygos. Between these levels the supracardinal 

 enters into the definite organization both of the adult postcava in 

 its postrenal division and of the azygos in its lumbar and part of its 

 thoracic segments, entirely replacing in these districts the primitive 

 postcardinal veins. The postrenal division of the adult postcava 

 is formed as the result of a secondary median fusion by means of 

 transverse anastomoses dorsal to the aorta of the postcaval portions 

 of the supracardinals, the primitive postcardinal veins not entering 

 into the formation of this portion of the main trunk of the adult 

 vessel. 



IV. A RECONSTRUCTION OF THE AXIAL VEINS IN THE LUMBAR 

 REGION OF A 16-MM. CAT EMBRYO 



It is not the purpose at the present time to describe again, 

 in detail, the development of veins in the cat. This we have 

 already done in a paper published in 1920, to which the reader 

 is referred. 3 The chief object which the present publication 

 has in view is to bring together all atypical forms of the 



2 Am. Jour. 'Anat., vol. 6 (Proc. Ass. Amer. Anat.). 

 'Anat. Rec., vol. 20. 



