SECRETION OF THE DUCTLESS GLANDS. 



889 



which probably, therefore, form an internal secretion. The pos- 

 terior lobe arises as an outgrowth from the floor of the third ven- 

 tricle of the brain, the infundibulum, which comes into contact 

 with the epithelial pouch forming the anterior lobe. The epithelial 

 cells of the latter soon show a differentiation into two parts, one of 

 which gives rise to the anterior lobe, while the other invests the 

 body and neck of the posterior or nervous lobe. To this latter the 

 special name of the pars intermedia has been given. When fully 

 formed the posterior lobe consists of two parts, the pars nervosa, 

 composed of neuroglia cells and fibers and ependymal cells, and an 

 investing layer of epithelial cells, derived from the buccal ectoderm 

 and known as the pars intermedia (see Fig. 299). 



Fig. 299. Median sagittal section through pituitary of monkey; semidiagrammatic 

 (Herring): a, Optic chiasma; b, third ventricle; c, g, pars intermedia; d, epithelium of pars 

 intermedia extending round neck of pars nervosa; e, pars glandularis seu epithelialis; /, intra- 

 glandular cleft, lying between pars glandularis (e) and pars intermedia (g) ; h, pars nervosa. 



In the pars nervosa characteristic hyaline or colloid bodies 

 occur and histological work makes it probable that this material 

 constitutes an internal secretion. According to Herring,* it is 

 formed from the epithelium of the pars intermedia. The cells of 

 the latter invade the pars nervosa, undergo a hyaline degeneration, 

 and are finally discharged into the cerebrospinal liquid of the third 

 ventricle. Investigations upon the physiology of the pituitary 



* Herring, "Quarterly Journal of Experimental Physiology," 1, 121, 161, 

 281, 1908. 



