DEVELOPMENT OF SUPRARENAL BODIES IN MAMMALIA. 85 



more regular oval or polygonal form. In regard to the em- 

 bryos of the twentieth, twenty-second, and twenty-fourth days, 

 of which I have sections, there is nothing special to mention, 

 except that the suprarenals become gradually larger, that the 

 medullary and cortical substances increase accordingly, and 

 that the cell groups in the cortex become more and more defi- 

 nite and the trabeculae between them finer. We now come to 

 the twenty-six-day embryos. Fig. 8 shows a transverse 

 section of the left suprarenal (s. r.) about in the middle of 

 the organ. The cortex {c,c) is already made up of definite 

 cell groups, although not yet divided into the different zones 

 found in the adult. The connective-tissue framework is now 

 so fine that each cell has its own special mesh, although not 

 so represented in the figure. Capillaries between the cell 

 groups are well formed. The differentiated medullary sub- 

 stance is not so far advanced as that of the cortical part ; it 

 is divided into irregular groups of cells, whose nuclei are 

 stained darker than those of the cortex. Its veins (v, v) are 

 very conspicuous. The connective-tissue capsule is well 

 developed. 



The sympathetic nervous masses {n, n) are now full of 

 distinct ganglion cells, supported in a connective-tissue 

 network. Scattered among the larger cells are smaller cells, 

 as at a. Fig. 9 shows a section of the same suprarenal near 

 its posterior end. It will be seen that the cortex (c,c) no 

 longer completely surrounds the medullary part, but is open 

 toward the inner side. If we trace it backward we shall find 

 it occupying less and less space in the section of the supra- 

 renal, and gradually confining itself to the outer side. 

 Finally, having greatly diminished in quantity, it separates 

 from the medullary part, and soon after ends on the ventral 

 side of the vena cava inferior. The diagrammatic longitudinal 

 section of the same part, shown in fig. 10 A, will make the 

 relations clear. The cortical substance (c) is present only 

 on the ventral side at the posterior end of the suprarenal ; 

 and, if it were possible to show this in the same figure, would 

 be also visible on the outside; while the medullary substance 

 (m.) is confined to the dorsal and inner region. Certain 

 parts of the medullary substance present very peculiar 

 features. I refer to the parts marked /?, jo in fig. 9. In 

 them, spindle and stellate connective-tissue cells are very 

 abundant, and, by the union of their processes, seem to 

 divide the whole space into irregularly polygonal areas. In 

 these areas there are placed a number of small cells, some- 

 what like those of the central part of the medullary sub- 

 tance, with which the part jo, /? is directly continuous. It 



