112 THE DUCTLESS GLANDS 



the " medulla " of the adrenals of higher vertebrates. It 

 consists of chromaphil cells. Thus in the Amphibia we have 

 transition stages between the single adrenal of higher verte- 

 brates and the total separation of the two constituents in the 

 Elasmobranch fishes (see Fig. 26 s.m., c.g.s.). 



4. Amniota 



In reptiles the "cortical" and "medullary" constituents 

 enter into closer relationship with each other than in lower 

 vertebrates. In some groups the chromaphil cells are arranged 

 mostly on the dorsal aspect of the gland, and only penetrate 

 to a small extent ; in others there is a considerable mixture of 

 the two elements. In the Crocodilia and the Chelonia, for 

 example, the relations of " cortex " and " medulla " are often 

 almost identical with those of birds (q. v.). 



A typical representation of the microscopical appearances 

 of the reptilian adrenal is given in Fig. 27. 



Birds show an intimate interlacement of the " Hauptstrange" 

 (cortical) and the " Zwischenstrange " or " Intermediar- 

 strange " (medullary), so that the latter occupy the meshes of 

 the former (see Fig. 28). 



Mammals, alone among animals, possess a true cortex and a 

 true medulla, the latter as a rule completely surrounded by 

 the former. 



The cortex has in all essential points the same structure 

 as its homologues in the lower vertebrates viz., the Haupt- 

 strange of birds, the "cortical" columns of Reptiles and 

 Amphibians, the corpuscles of Stannius of Teleosts, and the 

 inter-renal " of Elasmobranchs. It consists of rounded groups 

 or columns of cells with one or two vesicular nuclei, and con- 

 taining glistening fat -like granules. These granules become 

 blackened by osmic acid, and stain deeply with Sudan III. 

 and Scharlach R. They are dissolved by xylol, chloroform, 

 etc., and so, when these reagents are used in the preparation 

 of microscopical specimens, a vacuolated appearance of the 

 protoplasm results. 



The structure of the medulla is not so easy either to discover 

 or to describe, but we may say in general terms that it consists 

 of cell columns which are not so distinctly marked as those of 

 the cortex. The cell outlines are not so distinct as those of 

 the cortex, and the granules in the protoplasm have a great 



