THE SUPRARENAL GLANDS 445 



At the inner border of the zona fasciculata the connective tis- 

 sue bundles pass insensibly from the regular columnar arrange- 

 ment of this layer into a reticular maze. The resulting cell 

 groups are of very irregular form and compose the innermost cor- 

 tical layer, the zona reticularis. This layer is the thinnest and 

 least distinct of the three zones of the cortex. It can often be 

 more readily distinguished by the highly pigmented condition of 

 its cells, than by the mere form of its cell columns. In man it 

 passes almost insensibly into the medulla ; in many animals e. g., 

 the dog, cat, and pig there is a sharp demarcation between the 

 zona reticularis and the medulla, produced by a thin membranous 

 layer of connective tissue which apparently results from the fusion 

 of the central ends of the fibrous bands in the cortical stroma. 

 Such a membranous septum is usually wanting in the human 

 adrenal. 



The connective tissue stroma of the adrenal consists of a deli- 

 cate vascular network, which in the cortex contains very few if 

 any elastic fibres. Flint * has shown that this connective tissue is, 

 in large part, at least, a reticular tissue. The capsule consists of 

 dense bundles of white fibrous tissue among which are many elas- 

 tic fibres. The stroma of the medulla is also richly supplied with 

 elastic tissue. 



The epithelium of the zona glomerulosa is arranged in sphe- 

 roidal groups or in hooked or slightly coiled columns which are 

 continuous with the straight columns of the fascicular zone. The 

 cells of the zona glomerulosa are closely packed within the con- 

 nective tissue meshes and the cell outlines are very indistinct. 

 Wherever their outlines can be readily distinguished the cells are 

 seen to be of columnar shape and are arranged in slender columns 

 whose cells are often grouped about an indistinct central lumen. 

 The cytoplasm of the cells of this zone is finely granular and stains 

 readily with acid dyes. Occasional minute fat droplets appear in 

 the innermost cells of the group, but these are never so abundant 

 as in the more internal portions of the cortex. The nuclei in this 

 zone are spheroidal in shape and rich in chromatin ; they present 

 frequent mitoses (Canalis f),but these are more abundant in early 

 life than in the adult. 



The cells of the zona fasciculata are highly characteristic. They 

 are arranged in long straight columns which extend from the zona 



* Contrib. to the Sc. of Med. ded. to W. H. Welch, 1900. 

 f Internat. Monatschr. f . Anat. u. Physiol., 1877. 



