666 INTERNAL SECRETION ENDOCRINE GLANDS 



The functional difference between cortex and medulla is easily under- 

 stood when we reflect that the morphological history of the two tissues 

 is quite different. The medulla is developed from cells which push 

 their way into the gla id from the rudiments of the sympathetic ganglia 

 at that level, and is therefore of ectodermic origin. The cortex is 

 derived from the same mesodermic structure which gives rise to the 

 kidneys and genital organs. 



Embryologically, the cortical cells are related to the interstitial cells 

 of the ovaries and of the testes, and like these are characterized by their 

 richness in lipins (or lipoids). There is some evidence of an inter- 

 relation between the thyroid and all these groups of sex cells (interstitial 

 cells of ovary and testes, cortex of adrenal). Removal of a large part 

 of the adrenals in the rabbit causes slight though definite hypertrophy 

 of the thyroid and lymphoid hyperplasia. This is also seen in 

 Addison's disease in man. 



Pituitary Body or Hypophysis. In the pituitary body two parts 

 essentially different in origin and function may be distinguished: 



(1) The large anterior lobe, or pars anterior, consisting of epithelial 

 cells, many of which are filled with granules of the type seen in 

 glandular epithelium, and abundantly provided with bloodvessels; 



(2) the smaller posterior or nervous lobe, or pars nervosa, also 

 called the infundibular portion, consisting chiefly of neuroglia, the 

 whole connected with the floor of the third ventricle by a stalk 

 called the infundibulum. 



A further subdivision of the epithelial portion is made into the 

 anterior lobe proper and the pars intermedia or intermediate lobe, con- 

 sisting of epithelial cells, less granular and less richly supplied with 

 bloodvessels than those of the pars anterior. The pars intermedia 

 forms an epithelial investment of the pars nervosa, almost completely 

 surrounding it and throwing out offshoots of epithelial cells into its 

 substance, which is also invaded by colloid material secreted by the 

 cells of the intermediate lobe. The differences in the structure of the 

 anterior and posterior lobes of the pituitary body correspond to a 

 difference in their development. The anterior lobe is developed (in 

 man in the fourth week of intra-uterine life) from an ectodermal pouch 

 (Rathke's pouch), which is pushed up from the roof of the bucco- 

 pharyngeal cavity towards the mid-brain. The posterior lobe is 

 developed from an extension of the neural ectoderm, which grows back- 

 wards as the infundibular process till it meets and blends with that 

 portion of the buccal pouch which gives rise to the pars intermedia. 

 The pars intermedia is separated from the anterior lobe proper by a 

 cleft which represents what is left of the lumen of Rathke's pouch. 

 In connection with the interpretation of the results of experiments on 

 removal of the pituitary body, it is of consequence to remember that 

 a residue of the same epithelium which develops into the anterior lobe 

 appears always to get cut off in the vault of the pharynx, constituting 

 the so-called pharyngeal hypophysis, and consisting of a cord of cells 

 identical with those of the anterior lobe (Haberfeld). Embryonic 

 ' rests ' of hypophyseal tissue are also often found in the dura of the 

 sella turcica, in which the pituitary body lies, and in the body of the 

 sphenoid bone. Cells of the intermediate lobe also run up the stalk 

 of the infundibulum, and even stretch for a little distance along the 

 floor of the third ventricle. Add to this the formidable nature of the 



