DEVELOPMENT OF SUPRARENAL BODIES IN MAMMALIA. 83 



any more definite structure. Closely applied against the supra- 

 renal, on its inner side, there is a large mass of sympathetic 

 nerve cells {71). At its ventral end, a process of this mass, 

 partly composed of nerve fibres, enters the cortical substance 

 at the point {a). The nervous mass has very much the appear- 

 ance of the medullary substance — its nuclei being stained in 

 the same way — although there are no connective-tissue cells 

 visible in it. On tracing it forward it becomes continuous 

 with the main sympathetic cord dorsal to the aorta. Fio-. 6 

 shows a section immediately behind that represented in 

 fig, 5. Here we see the branch (a, fig. 5) of the nervous 

 mass (n) passing into the suprarenal and uniting with the 

 medullary substance (m), a relation which affords strong 

 presumptive evidence that the latter is derived from the 

 nervous mass without. To demonstrate this point still 

 more conclusively I have introduced here a figure (fig. 7) of a 

 section of the suprarenal of an embryo rat about 23 milli- 

 metres long. In this figure there are to be seen nerve 

 fibres {b) starting from the nervous mass (71) and entering the 

 suprarenal (s. r). Amongst the fibres numerous cells (m), 

 that look exactly like those in the mass (?^),^ have found their 

 way into the middle of the suprarenal, and are clearly dis- 

 tinguishable from the surrounding cortical cells (c, c) as well 

 by the structure of the cell groups as by their darker stain- 

 ing. In several sections, continuous with the one figured, 

 strands of nerve fibres dividing from the main bundle may be 

 seen proceeding into various parts of the suprarenal, and 

 wherever they go, they are followed by nerve cells. That 

 these cells become the medullary substance there can be 

 no doubt, as I have seen the parts occupied by them stained 

 brown by bichromate of potash in somewhat older rabbit 

 embryos. I ought to add that the mass (^ti) is continuous 

 with the main sympathetic cords. 



As we trace the sections of the sixteen-day embryo 

 rabbits backward, we find the nervous mass (;z, figs. 5 and 6) 

 gradually spreading towards the ventral side of the aorta, 

 and there constituting what must be regarded as a sympa- 

 thetic plexus. This plexus seems to join the medulla of the 

 suprarenal at more than one point. The medullary sub- 

 stance continues to the posterior end of the suprarenal, 

 occupying irregular areas more or less in the centre. 

 Towards the posterior termination it occupies by far the 

 larger portion of a section of the suprarenal, and is covered 



* The engraver has unfortunately not represented the nuclei of the mass 

 («) very satisfactorily ; so that tlieir similarity wiih those of the medullary 

 substance is not obvious. 



