DEVELOPMENTAL CHANGES IN THE EARLY EMBRYO 



141 



It is believed that the more anterior infundibulum will form the 

 pars nervosa or posterior pituitary gland. The more posterior hypoph- 

 ysis can be identified as contributing to the anterior pituitary gland 

 (pars distalis, pars intermedia, and pars tuberalis of mammals). At 

 the most ventral aspect of the forebrain, in the floor, is a pronounced 



Infundibulum 

 Epiphysis 



Hypophysis 



Thyroid 



Photograph of endocrine anlagen at the 5 mm. stage 

 of the frog tadpole. 



thickening known as the optic chiasma, anterior to which is a de- 

 pression associated with the lateral optic vesicles. The depression is 

 the optic recess (recessus opticus) which is connected with the optic 

 stalk. Anterior to this, also in the floor, is a second thickening known 

 as the torus transversus which becomes the seat of the anterior and 

 other commissures. This structure lies within the more extensive 

 lamina terminalis, which represents the fused anterior neural folds 



Tail fin Tuberculum posterius 



Sub-notochordal rod ..„„.„„„. \ ^fesencephalon 



Epiphysis 



Neurocoe 



Proctodeum (anus) 

 Yolk 



Mesoderm 



Hypophysis 



. , Optic recess 

 id \ 



Heart Optic chiosmo 



Pericardial cavity 



Liver diverticulum 

 Reconstruction of the 5 mm. tadpole in sagittal section. 



