^6 K. MITSUKURI. 



former exhibits also a subdivision into three more or less 

 distinct layers. Starting from the outside, they are (1) a 

 rather thin greyish layer ; (2) yellowish layer comprising 

 the main mass of the organ, and showing, even to the naked 

 eye, radial striation ; and (3) a layer, of a much darker 

 yellow, adjoining to the medullary substance. These layers 

 are for the most part arranged concentrically ; but at the 

 posterior end there is a modification in their relations, which, 

 singularly enough, seems to have hitherto escaped observa- 

 tion. The medullary substance, instead of being covered 

 by the cortical layers, as in other parts, here becomes 

 attenuated into a narrow streak, and reaches the outside. 

 Roughly speaking, therefore, the cortical substance is in the 

 shape of a horseshoe, completely surrounding the medullary 

 part, except at one point at the posterior end. The histo- 

 logical structure of this part is of great interest, as will be 

 seen further on, on account of the peculiar developmental 

 history of the medullary substance. A section of the supra- 

 renal body across its shorter diameter will show three layers 

 in concentric rings. 



Fig. 1 shows a part of a transverse section of the supra- 

 renal considerably magnified. If the whole section had been 

 figured the outline would be oval, and the medullary sub- 

 stance (m), of which only a small portion is represented, 

 would occupy a rather large irregularly oval area in the 

 centre. In the figure, however, are shown all three parts 

 of which the suprarenal is composed, viz. (1) the outer cap- 

 sule of connective tissue (d), (2) the cortical substance 

 {a,b, c), and (3) the medullary substance (m). I shall 

 briefly describe each of these three portions. 



Of the connective tissue capsules I need only say that 

 nerves and blood-vessels are found embedded in it in toler- 

 able abundance, and that bundles of connective- tissue fibres 

 from the capsule are sent inwards to form the framework 

 of the whole organ. 



The whole space between the outer capsule and the medul- 

 lary part is occupied by the cortical substance, which, there- 

 fore, constitutes the main mass of the organ. Briefly speaking, 

 it is made up of large cells, supported in a very fine network 

 of connective tissue^so fine that each cell has its own cavity 

 in the mesh. These cells are collected into groups by coarser 

 trabeculae, and the forms these cell groups assume in diff'erent 

 layers give characteristic appearances to any particular layer. 

 We thus recognise in the suprarenals of the rabbit three 

 distinct zones (a, b, c, fig. 1), which correspond to the 

 three layers visible to the naked eye (see above). The outer- 



