40 ANATOMY 



adrenals of certain other large mammals (rhinoceros, hippo- 

 potamus, giraffe) also show this lobulation to a lesser extent. 

 The adrenal of the porpoise is characterized by an irregular 

 surface and when sectioned gives the appearance of cerebellar 

 tissue due to many strands of connective tissue which pene- 

 trate the cortex from the capsule. 



THE CORTEX 



Although considerable variation exists in the cellular ar- 

 rangement of the adrenal cortex in different species, a more or 

 less general pattern is present according to which the cortex 

 is divided into three zones: the glomerulosa, fasciculata, and 

 reticularis (Figures 4, 5, and 9). The layer beneath the cap- 

 sule is known as the zona glomerulosa and consists of cells ar- 

 ranged in rounded groups with an indication of an alveolar 

 structure. The cells of this zone are usually very granular 

 and stain deeply. The zona fasciculata is continuous with the 

 glomerulosa and consists of columns of cells arranged radially. 

 This zone in most species is very rich in fat. The innermost 

 zone of the adrenal is known as the reticularis because of the 

 irregular arrangement of its cells. This zone is in contact and 

 to some extent interlaced by strands of the chromaphil tissue 

 of the medulla. 



The above described division of the cortex into zones is not 

 clearly defined in all animal species and is probably only of 

 morphological significance. The cause for this peculiar ar- 

 rangement of the cells is probably a combined effect of the 

 manner in which the cortical cells are constantly being re- 

 newed during life and the restraining influence of the capsule 

 and connective tissue framework of the gland. New cells are 

 constantly being formed in the inner glomerulosar and outer 

 fascicular zones and removed from the reticular zone. The 

 pressure of the newly formed cells in the vicinity of the glomer- 

 ulosar-fascicular boundary would tend to compress the cells 

 on the surface thus giving the glomerulosa its characteristic 



