ORGANS OF NEURAL EXCRETION 101 



maintained in post-natal growth and life, and the role 

 of that body, in its association with the production of 



FIG. 31. SIDE VIEW OF THE HEAD OF AN EMBRYO-CHICK OF THE THIRD 

 DAY. (From Balfour.) 



CH, cerebral hemispheres ; FB, thalamencephalon ; MB, midbrain ; C6, cerebellum ; 

 HB, medulla oblongatae ; N, nasal pit ; of, auditory vesicle not yet closed 

 externally ; op, optic vesicle, with /, the lens, and cfif, the choroidal fissure (in 

 mesoblast) ; IF, the first visceral fold or plate, the superior maxillary fold slightly 

 indicated above it ; 2, 3, jF, the second, third and fourth visceral plates with 

 the visceral clefts between them. 



certain diseased conditions, becomes highly suggestive 

 when we continue to enquire more deeply into its bear- 



FIG. 32. VERTICAL SECTION OF THE INFUNDIBULUM AND PITUITARY 

 DIVERTICULUM IN THE RABBIT'S EMBRYO, AFTER THE OPENING OF 

 THE FAUCES. (From Mihalkovics.) 



For the earlier stages see Fig. 30, p. 100, A and B. be, dorsum sellae ; if, infundi- 

 bulum ; tha, floor ot thalamencephalon ; py, pituitary diverticulum, now closed ; 

 p' stalk of original communication with the mouth ; ph, pharynx ; ch, notochord 

 in the spheno-occipital part of the cranial basis. 



ings. The earliest stage at which the human embryo 

 shows that evolution of the pituitary gland has begun 

 is when a superior and posterior diverticulation of the 



