414 



THE ORGANS 



represent rudimentary ganglion cells and a few nerve fibres. In the 

 human embryo, and in many adult lower animals, the nervous 

 elements are much more prominent and more definitely arranged. 

 Thus Berkley describes the posterior lobe of the pituitary body of the 

 dog as consisting of three distinct zones: (i) An outer zone of three 

 or four layers of cells resembling ependymal cells, connective-tissue 



e f 



Fig. 2Q2. — Mesial Sagittal Section through Pituitar\' Body of Five Months Human 

 foetus. (Herring.) a, Optic chiasma; b, anterior extension of pituitary body; c, third 

 ventricle (infundibulum) ; d, pars anterior; e, neck or isthmus of pars nervosa connecting 

 it with bottom of infundibulum; /, epithelium continuous with pars intermedia sur- 

 rounding neck; g, intcrglandular cleft; h, pars nervosa or posterior. 



septa from the capsule separating the cells into irregular groups. (2) 

 A middle zone of glandular epithelium, some of the cells of which are 

 arranged as rather indefinite alveoli which may contain colloid. This 

 is termed the pars intermedia. (3) An inner layer of nerve cells and 

 neuroglia cells. These react to the Golgi stain, the nerve cells hav- 

 ing axones and dendrites. Most of the axones appeared to pass in 

 the direction -of the infundibulum, but could not be traced into the 

 latter. The posterior lobe is of ectodermic origin, developing as a 



