ON THE SUPRA-RENAL, THYMUS, AND THYROID BODIES. 67 



blastema arranged in minute lobular masses around the ante- 

 rior parts of the cardinal veins of Kathke, surrounding the 

 jugular veins and ductus Cuvieri for a short distance behind 

 the forepart of the Wolffian bodies. Immediately in front of 

 the Wolffian bodies these lateral masses of blastema are narrow, 

 being scarcely perceptible on the coats of the cardinal veins ; 

 but around the ductus Cuvieri they are larger, and differ from 

 the general texture of the embryo, in having a darker colour, 

 in containing no fibres, in separating readily from the sur- 

 rounding parts, and in their lobulated appearance. They 

 extend forwards nearly to the base of the cranium, and are not 

 connected across the median plain. They are broadest at the 

 sides of the heart, and when the pericardium is opened, are 

 seen through its posterior wall occupying the future situations 

 of the lungs, which at the period stated exist as two small 

 lobulated white bodies, projecting from the intestinal tube, 

 behind and below the heart. 



These two lateral masses are the only remaining portions 

 of the membrana intermedia : the posterior portion on each 

 side, on the inner aspect of the anterior extremity of the 

 Wolffian body, becomes the supra-renal capsule ; the enlarged 

 middle portion and the outer part of the cervical portion 

 become the thymus ; w r hile the internal anterior part resolves 

 itself into the thyroid body. These three organs are therefore 

 at this period continuous with one another on each side of the 

 middle line, no isthmus having yet been formed. They are 

 also continuous with the Wolffian bodies ; these bodies, the 

 supra-renal capsule, the thymus, and the thyroid, forming a 

 continuous mass, situated in the elongated angular channel, 

 which stretches from the cranium to the coccyx on the outside 

 of the intestinal or mesenteric laminae, and between them and 

 the visceral laminae. 



The Wolffian bodies are the last organs formed out of the 

 membrana intermedia, which assume a special structure. The 



