238 The Development of the Vena Cava Inferior 



of 21 mm. a single one of them remained on either side above the an- 

 astomosis X. The relations of the vessels in this region are shown in 



Fig. 9, the section on 



_. the right side passing 



t ^l "" , . through the fused sub- 



'■ I """ cardinal and cardinal. 



''i^^ /-// A '' The inferior sections of 



\// ? ^ , the subcardmal veins no 



> ( longer receive branches 



K^ ^ ^ ' '-) ' ^'['' ^ —'^■^- from the Woli!ian 



34 ' ' \ c^ bodies, but appear as 



j;''.,_ ,\. J r''^-^'^^ large spaces in the 



V; " '^ OP^ . , ' ^,3/^"""^ mesentery, conspicuous- 



/txT^^^ 'r^ ' f /^^ '^•'^^- ^-' empty of corpuscles, 



WR-i^^r^'i)^/ -.4^ ^^'''''^^' *^'' adjoining 



• ^' \\(l^^j \ I ^ The mesenchyma in 



;\ /ll W l^ c-^ -..i front of the aorta below 



GA.' 'Mes. the anastomosis X is per- 



FiG.lO. Rabbit embryo of 14.5 mm., 14 days, 18 hours (?). meated by these SpaceS, 

 Series 143, section 857. X 45. The vessels shaded with -i • T?' 1 n 



lines contain corpuscles : the others are empty. AS SllOWll 111 J-'' Ig- if. 



Mere strands of mesen- 

 chyma separate them from one another and the adjoining veins. Their 

 fate is unknown, but they recall the description by Sala, oo, of the 

 anlages of lymphatic hearts in the chick. They pass into slender ves- 

 sels, empty of corpuscles, which extend some distance cephalad from the 

 anastomosis X. They appear in the position previously occupied by the 

 lower part of the subcardinal, and at the time when those vessels dis- 

 appear. Therefore the}' may be subcardinal derivatives. 



On the left side, the superior part 

 of the subcardinal vein l)egins as a con- "^^^ N 

 siderable branch from the Wolffian "^^c^-^- H^^^*^ 



body, uniting with another from the "^^-^^^^^===4 X'^^^^ 



suprarenal area. It receives vessels from ^.r"^^^^!-, ) 



botli structures along its course. The A.M.''^^^^^ \""^'^F' 



size of this i)art of the left subcardinal pip,. n. Keconstruction from rab- 



in a 21 mm. rabbit is shown in Fig. 11, Wt embryo of 21 mm., 17 days, series 



drawn with the same magnification as 



Fig. 8, PL IT. The suprarenal body is found between the cardinal and 



subcardinal veins which lie very close to it, the cardinal at the dorsal 



