24 TISSUES AND ORGANS 



Golgi's method ; and secondly, cells closely resembling the 

 chromophobe elements of the pars anterior. 



The pars tuberalis is only a small structure in man, but is of 

 great histological interest, because in it may be seen structures 

 closely resembling the cell-nests found in epitheliomata. 



The pars posterior is a nervous mechanism in which typical 

 ependymal elements, mossy neuroglial cells and certain large 

 pyramidal cells of uncertain nature can be found. If the last- 

 named are nerve cells, they certainly differ from any others^ 

 inasmuch as they contain no Nissl granules. In man only one 

 type of cell is numerous ; this is a more or less fusiform element 

 with fragile indistinct process running off from it. Nerve fibres 

 enter the pars posterior from the supra-optic nucleus and form 

 complex whorls around blood vessels or around groups of cells. 

 Some end in hyaline masses, whilst others have an end-bulb 

 reminiscent of that seen at the end of a regenerating nerve fibre ; 

 the former structure is not found in the human subject until about 

 the second year of life. 



The pathology of the pituitary gland is far better understood 

 from the clinical than from the histological aspect, for, although 

 many changes are known, few have specific characters. In 

 acromegaly there is almost invariably a definite adenoma com- 

 posed entirely of eosinophilic, i.e., chromophilic cells, whereas the 

 usual adenomata of this organ consist of chromophobe cells and 

 are not accompanied by acromegaly. 



THYROID 



It is very difficult to determine how much of the recent work 

 on this important endocrine gland should be mentioned here ; 

 much of it is of the greatest practical imj^ortance, although not 

 strictly within our present purview. The structural unity of the 

 thyroid gland is the individual follicle, although some writers 

 contend that the unit is really a system of closed tubes suspended 

 in a lymph sac. One of the most interesting elements in the 

 organ are the inter-follicular epithelial cells which, in man, normally 

 form small groups in the inter-follicular stroma, particularly in 

 late foetal life and in infancy. These cells are normally destined 



