354 The Histogenesis of the Adrenal in the Pig 
surface of the Wolffian body with the mesenteric attachment. In the 
early stages it lies entirely ventral to the glomerular or mesonephric 
branches of the aorta, but as it increases in size these vessels transfix it. 
It is clearly differentiated from the neighboring structures, not by any 
distinct capsule, but by young connective tissue more or less condensed 
and concentrically arranged. It extends as a column of cells in an 
antero-posterior direction a distance which roughly corresponds with the 
anterior one-third of the Wolffian body, falling short, however, of the 
anterior extremity of that body. In the posterior direction it is hmited 
by the posterior cardinal veins: these veins run forward, one on each side, 
along the medial aspect of the Wolffian body, and are connected by 
several cross anastomoses, the last of which about corresponds to the 
junction of the anterior with the middle one-third of the Wolffian 
body. At this point the left vein virtually bifurcates, sending one 
division into the Wolffian body of the same side, while the other crosses 
the median line to open into the right cardinal; the latter soon bifur- 
cates in its turn, one division entering the Wolffian body of its side, the 
other joining the primitive inferior vena cava. F. T. Lewis,” in the 
course of an interesting account of the development of the inferior vena 
cava, has suggested that the term “subcardinal” should be applied to 
the portions of these veins which lie posterior to the anastomoses. 
Immediately anterior to the most anterior of the anastomoses the caudal 
extremity of the anlage is encountered. The cells composing it have a 
moderate amount of finely granular cytoplasm, which possesses con- 
siderable affinity for acid dyes; their nuclei are vesicular, and contain 
a fair amount of nuclear sap and some chromatin granules. At this 
stage capillaries are beginning to make their appearance in the anlage. 
Ventral to the anlage and running lateralward on the ventral surface 
of the Wolffian body is a thickening composed, in the main, of mesen- 
chymal cells and blood vessels; it is continuous with the connective tis- 
sue framework of the Wolffian body, and is lined superficially by tall 
coelomic epithelial cells. In these cells mitotic figures are not infre- 
quent, and in some of them, at least, the plane of cleavage is parallel 
with the surface. This epithelium, in many situations, is wrinkled or 
furrowed, and cells are invaginated here and there into the subjacent 
tissue either singly or in small collections; none of these invaginations, 
however, directly reach the anlage of the adrenal. The thickening is 
coextensive in the anterior direction with the adrenal; in the posterior 
direction it is immediately continuous with the anlage of the genital 
1 Am. Jour. Anat., Balt., Vol. I, pp. 229-245. 
