The Comparative Histology of the Suprarenal Capsules. 311 



The structure of the mammalian cortex is tolerably easy to make 

 out and is fairly well-known. But it will be desirable to give a brief 

 account of it, so that it may be compared with its homologues in the 

 lower Vertebrata. 



In man, as was first pointed out by Arnold [2], the cortex is 

 seen on section to consist of three layers, more or less distinct from 

 each other, but not nearly so much so as are cortex and medulla 

 from each other. The outermost layer is called the ^ona glomerulosa, 

 as the cells are aggregated into rounded masses. Beneath this is the 

 zona fasciculata, so-called from the elongated columns of cells which 

 form it. Internally, adjoining the medulla, is the zona reticularis, 

 this name indicating an approximation to a network arrangement of 

 the cortical columns in this layer. 



These three layers are however only arbitrarily separated off from 

 each other. It seems clear that the "zona glomerulosa" is nothing 

 more than the columns of the "zona fasciculata" which turn round 

 when they come near the surface of the gland and run for a greater 

 or less distance parallel to the capsule. In a radial section these 

 portions are of course cut transversely and appear as rounded masses 

 of cells. 



This arrangement into three layers can be tolerably well made 

 out in the guinea-pig, the ox, and the dog. In the rabbit the "zona 

 fasciculata" sometimes runs to the surface, or there is only a very 

 narrow "zona glomerulosa" with a wide "zona reticularis". 



The zona fasciculata is always more faintly stained than either 

 of the other layers. 



In some animals, as the horse and the ox, the cells in the outer- 

 most layer of the cortex do not always appear as circular masses, 

 but are sometimes arranged as crescents or horse-shoes, and sometimes 

 the ends of the crescent become fused and a ring of cells is formed, 

 presenting an appearance closely resembling that of a gland alveolus 

 with a large lumen. But this is not a true lumen, as appears from 

 the fact that it sometimes contains tissue of the same nature as the 

 stroma of the gland, and occasionally even blood-vessels may be ob- 

 served in it. 



