. The American journal of anatomy. ions thereon, that the medulla is derived fromthe same source as the cortex. Josef Wiesel° employed pig embryos 1 cm., 2 cm., cm. and 3 cm. Ueber die Entwickelung der Nebenniere des Schwaines besonders der Marksub-stanz. Anat. Hefte, Wiesb., 1901, Bd. XVI, S. 115-150. E. H. Whitehead 353 long for the study of the cortex. He detected the anlage first in pigsof 2 cm. in the shape of a projection on the medial side of the Wolffianbody. Ventral from this projection, he says, the coelomic epithelium ishighly developed; it shows, however, no differentiation, be
. The American journal of anatomy. ions thereon, that the medulla is derived fromthe same source as the cortex. Josef Wiesel° employed pig embryos 1 cm., 2 cm., cm. and 3 cm. Ueber die Entwickelung der Nebenniere des Schwaines besonders der Marksub-stanz. Anat. Hefte, Wiesb., 1901, Bd. XVI, S. 115-150. E. H. Whitehead 353 long for the study of the cortex. He detected the anlage first in pigsof 2 cm. in the shape of a projection on the medial side of the Wolffianbody. Ventral from this projection, he says, the coelomic epithelium ishighly developed; it shows, however, no differentiation, being similarto the epithelium of the coelomic cavity in general. This finding, hethinks, warrants the conclusion that the cortex is derived from thecoelomic epithelium. Of the medulla Wiesel makes a thoroughstudy. He traces its origin back to the sympathetic ganglia, and de-scribes the passage of medullary cells in collections through the cortexto the vicinity of the central vein in the way previously described byFlint. % -^. Fig. 2. Pig 13 mm. Leitz obj. 3, oc. ; W. b., WolflSan body. Ad., adrenal; G. r., genital ridge, lies., It will be convenient to consider the genesis of the cortex and medullaseparately, as they are separated by a considerable interval of time. The Histogenesis of the Cortex, Although the anlage appeals at a much earlier stage, it will be con-venient to begin the observations in an embryo of 13 mm. and trace ittowards its beginning. In such an embryo (Fig. 2) the anlage con-sists of an ovoid collection of cells situated ventro-lateral from the aortaand dorsal from the angle formed by the junction of the ventral 354 The Histogenesis of the A(h-eiiiil iu the Pig- surface of the Wolffian lx)dy witli the mesenteric attachment. In theearly stages it lies entirely ventral to the glomerular or mesonephricbranches of the aorta, but as it increases in size these vessels transfix is clearly differentiated from the neighboring structures, not
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