The Development of the MammaHan Pituitary Body 163 



immediate relationship with the brain, and cannot therefore act upon it in 

 this manner. 



The most complete account of the early development of the pituitary 

 body is that given by Mihalkovics (21), who investigated the subject in 

 rabbit and chick embryos. Mihalkovics found that the anterior lobe is 

 developed from Rathke's pouch, which, in mammals as in amphibians, is 

 of ectodermic origin. The beginning of the pouch or hypophysial angle 

 lies in front of the oral plate, where the epidermis bends round the base of 

 the brain to the nasal mucosa. In the rabbit, Mihalkovics states that the 

 end of the notochord is in contact with the epidermis at the back of 

 Rathke's pouch. When the oral plate ruptures, its upper stump, con- 

 taining in its upper part the head of the notochord, bends forward and 

 narrows the mouth of the epithelial pouch, leading to the formation of a 

 definite sac — the hypophysial sac. The wall of the sac presses upon the 

 base of the anterior brain vesicle, giving rise at its upper extremity to a 

 fold in the wall of the brain which becomes the primitive infundibulum. 

 Mihalkovics denied that the end of the notochord is ever united to the wall 

 of the fore-brain ; it does not enter into the formation of the infundibulum 

 at all, but has some influence upon the hypoph3\sial sac, by preventing this 

 from extending backwards. The primitive infundibular process comprises 

 the surrounding tissue of the tuber cinereum as well as the origin of 

 the infundibulum, and the true infundibulum is formed at a later stage 

 by its own growth from a portion of the primitive infundibular process. 

 Mihalkovics made a careful investigation of the relations of the notochord, 

 and found that its head touches the lower part of the posterior wall of the 

 hypophysial sac in rabbits, but is placed at a higher level in birds ; it 

 exercises no traction upon the sac in either, and, beyond presenting a 

 barrier to the backward growth of the sac, takes no part in the formation 

 of the pituitary body. 



The main conclusions of Mihalkovics' researches have been confirmed 

 by Kolliker (16), Kraushaar (18), Minot (22), Kupf f er (19), Salzer (33), 

 and others. Kupf f er described an additional origin of part of the anterior 

 lobe of the pituitary from the entoderm of the fore-gut. According to 

 Kupffer, the pituitary body of amphibians is built up from three separate 

 sources : part of the epithelial lobe is derived from Rathke's pouch, and 

 part from the anterior end of the fore-gut, while the infundibulum is of 

 brain origin. In mammals, e.g. the sheep, the hj^ophysial pouch appears 

 behind the " Riechplakode." Behind this and ventral to it is a swelling, 

 the " Haftscheibe," which is an important larval organ in Lepidosteus. 

 Then comes the double-layered oral plate (" Rachenhaut "), and behind 

 this an outgrowth of entoderm directed dorsally and forwards, known as 

 Seessel's pouch. The third portion of the pituitary, the cerebral, appears 

 later, after the disappearance of the oral plate and median "Riechplakode." 

 In the next stage the growth of entoderm increases, but is cut oft' from 

 Seessel's pouch ; no cavity is to be found in it, and the end of the notochord 



