ss 
however, simply displaced fibrils which result from the agitation of 
the section in washing out the debris. Like the septa of the Zona 
glomerulosa, those of the medulla often appear as homogeneous pro- 
cesses but can be shown, in frozen sections or sometimes by the 
higher powers of the microscope, to consist of aggregations of fibrils, 
cut in parallel segments or as a delicate crosshatch when the fibrils 
interlaced. These septa embrace the medullary cell groups entirely 
and are considered by the earlier investigators to be the membranae 
propriae of the medullary “Schläuche”. Sometimes the septa in digested 
paraffin sections are cut horizontally (Fig. 7, e) and show the fibrillar 
structure of the septa. 
ARNOLD described two layers in the medulla which showed dif- 
ferences in the arrangement of the interstitial tissue and cell groups. 
This apparent stratification is due, however, to the distribution of the 
smaller veins in the peripheral portion of the medulla which renders 
the cell groups in that region more distinct. The medulla, as a whole, 
is arranged on a uniform plan and excepting for the distribution of 
the veins the groups in the central have relations similar to those in 
the peripheral portions. 
The veins of the medulla are provided with a sheath of reticulum 
(Fig. 7, v), to which the septa surrounding the cell groups are at- 
tached. Thus, in thick sections prepared by Matu’s method the course 
of the veins is clearly marked out in the reticulum to that beautiful 
negative pictures of the venous tree are obtained. Clear spaces in 
the reticulum bounded by definite walls indicate the course of the 
veins and circular strands of reticulum traversing these spaces show 
where branches of the venous tree leave the plane of section and turn 
down into the depths. 
Resumé. 
1) The framework of the adrenal is made up of reticulum. 
2) The reticulum of the Zona glomerulosa in the dog is composed 
of septa derived from the capsule which divide the outer layer of the 
cortex into oval or oblong spaces that contain the coiled columns of 
cells forming that zone. Smaller processes of reticulum pass in and 
separate the columns from each other. 
3) The reticulum of the Zona fasciculata consists of processes 
and fibrils running at right angles to the capsule from the Zona 
glomerulosa to the Zona reticularis. The fibrils pass in and out 
between the cells of this layer and are frequently gathered into 
small processes that sustain the relations of the cell columns of 
this zone. 
