ON THE SUPRA-RENAL, THYMTJS, AND THYROID BODIES. 75 



in not being divided into lobules, in having the groups of cells 

 of which it consists separated from one another by moderately 

 strong capsular membranes, and in being more vascular, the 

 anterior and venous trunks being much larger. 



The supra-renal capsules also consist of nucleated cells 

 grouped round germinal spots, and arranged, not in lobules, 

 but in columns passing towards the surface of the organs ; an 

 arrangement corresponding to the radiating direction of the 

 veins, and the converging arteries of these parts. The supra- 

 renal and thyroid bodies are more vascular than the thymus 

 from being developed around large arteries, while the thymus 

 is in connection with smaller trunks, the former being de- 

 veloped in connection with the first and second aortic arches 

 and the omphalo-mesenteric vessels ; the latter in connection 

 with the internal mammary arteries and other small thoracic 

 and cervical branches. The greater density of the areolar 

 capsule of the thyroid may probably be explained by this in- 

 creased vascular supply. 



That portion of the membrana intermedia which is sepa- 

 rated from the rest of the membrane, and included in the body 

 of the embryo by the umbilical constriction, and which has 

 not already been devoted to the formation of the heart, liver, 

 pancreas, and external portion of the intestinal canal, is found 

 massed along the trunks of the primitive venous system, the 

 sides of the arches of the aorta, the terminal portion of that 

 vessel, and the origins of the omphalo-mesenteric arteries. 



The portions of the membrana intermedia which are last 

 of being converted into special organs, the Wolffian bodies, are 

 the parts which project one on each side of the aorta, along 

 the posterior part of the cardinal veins of Eathke, between 

 the intestinal plates and visceral laminae. 



The portions of the membrana intermedia which remain 

 between the upper extremities of the Wolffian bodies and the 

 heart and liver, and which surround the origins of the om- 



