The Development of the Mammalian Pituitary Body 165 



theory that the glandular hypophysis was originally the coxal gland of 

 Arthi'opoda. 



Kupffer's description of the threefold origin of the pituitary body has 

 received support from observations by J. Nusbaum (24) and Saint- 

 Remy (31). Nusbaum found that in dog embryos of 9 mm. Seessel's 

 pouch is well developed, and its anterior extremity abuts against the 

 posterior wall of Rathke's pouch. In 80 per cent, of older embryos examined 

 it gives rise to a column of cells which unites with the epithelium of 

 Rathke's pouch, and thus enters into the formation of the anterior lobe. 

 In the remaining embryos no such appearance is seen, and the anterior 

 lobe is entirely ectodermic in origin. • Traces of a lumen were noticed by 

 Nusbaum in the column of cells growing from the fore-gut, but not a 

 definite communication between the interior of the buccal invagination and 

 the fore-gut. The connection is not preserved for long, and the entodermic 

 cells disappear, with the exception of a few which join the posterior 

 wall of Rathke's pouch. What further part these cells play — if any — in 

 the formation of the anterior lobe of the pituitary Nusbaum did not 

 determine. 



Saint- Remy (31) described a budding of Seessel's pouch in the embryo 

 chick towards the seventieth hour of incubation. The bud acquires a fine 

 lumen, and, reaching Rathke's pouch, afibrds a direct communication between 

 the interior of the latter and the fore-gut. The connection lasts a little, 

 then disappears, the cells of Seessel's pouch never actually uniting with 

 those of Rathke's pouch. Saint-Re my agrees with Kupffer that the 

 entodermic origin is rudimentary in birds and mannnals, and does not enter 

 into the formation of the adult pituitary body. It is, however, of morpho- 

 logical importance, and betokens the existence in lower forms of vertebrates 

 of a communication between the intestine and the buccal invagination. 



Dohrn (7) looked upon the pituitary as the remains of a preoral gill- 

 cleft. Salvi (32) has brought forward evidence in support of this view, 

 and states that in reptiles part of the pituitary is developed from the walls 

 of the premandibular cavities, which he believes to be the representatives 

 of gill-clefts. Valenti (34) describes the origin of the anterior lobe in 

 amphibians from an invagination of the fore-gut arising some distance 

 behind Seessel's pouch. The invagination, he considers, has not the signifi- 

 cance attributed by Kupffer to Seessel's pouch, but is rather to be regarded 

 as the representative of a gill-cleft. Valenti therefore supports Dohrn 's 

 theory. Dohrn 's view was based chiefly upon the assumption of a bilateral 

 origin of the anterior lobe of the pituitary. Dohrn himself described a 

 bilateral origin in Hippocampus, and Gaupp (10) found something similar 

 in reptiles. Gaupp, however, described a median origin in addition to 

 lateral ones, and believes all to be formed from the buccal cavity. 



Yet another interpretation of the significance of the pituitary has been 

 put forward by Beard (4), who believes the anterior lobe to be homologous 

 with the permanent mouth of Annelids. 



