The Development of the Maininalian Pituitary Body 



177 



brain, and its secretion, if it is a secretory structure, passes into the third 

 ventricle through the infundibuluin. For this reason Rabl-Ruckhard 

 (25) called it an infundibular gland. No such structure is found in 

 mammals, but Retzius (30) has described in them a slight swelling in the 

 form of a clover leaf appearing on the surface of the brain behind the 

 infundibulum, which he called the eminentia saccularis, and believed 

 to be the homologue of the saccus vasculosus of fishes. Retzius 

 described its external appearance only. In section, it is found to be a 



Fig. 8. — ^lesial sagittal section through developing pituitary body of ox. Drawing 

 from a i)hotograph. 



a, toiifiue-like process of epithelium spreadiiiK forwards; b, third ventricle; c, anterior lobe; d, epithelial cleft ; 

 (', epithelium of pars intermedia ; /, posterior lobe ; g, large lymph space extending into body of ossifying 

 sphenoid bone. 



thinning of brain substance in the tioor of the third \ entricle in front of 

 the corpora mainillaria. It is doubtful if this eminence is really homo- 

 logous with the saccus vasculosus of fishes ; it is not in the position one 

 would expect, and should be sought rather in the postero-superior angle of 

 the posterior lobe of the pituitary, where the blood-vessels enter, and where 

 there is fre(|uently in the cat, during development, the vascular knob 

 already mentioned. 



Although the mammalian brain has no saccus vasculosus, the posterior 

 lobe of the pituitary possesses an investment of epithelium which difiers 



