DEVELOPMENT OF SUPRAPERICARDIAL BODY 407 



the postbranchial body with the epithelial derivatives (epithelial 

 bodies III and IV) of the gill-pouches. Maurer ('87) describes 

 in Amphibia a derivative of the pharynx posterior to the last 

 gill-pouch which he calls the postbranchial body and considers 

 this as the homologue of the suprapericardial body. Greil ('05) 

 found that the postbranchial body of Maurer developed, in 

 amphibia as in selachians, from the ventral extremity of a rudi- 

 mentary sixth pouch and believes for this reason that the body 

 is ultimobranchial. In the higher vertebrates an homology with 

 the suprapericardial body is difficult to make because of the 

 rudimentary development of the pharyngeal pouches. In his 

 later communication, van Bemmelen believes that the 'Body 

 Y' of Mall ('87) in birds and the 'lateral thyreoids' of Born 

 ('83) and His ('80) in mammals are homologous with the supra- 

 pericardial body. Later writers, — Rabl ('07, birds), Grosser ('10, 

 man), and particularly Verdun ('98, mammals) describe a diver- 

 ticulum arising from the pharynx near the connection of the 

 fourth pouch. This body unites with the thyreoid and forms a 

 small cyst which, in some forms, contains colloid (Hermann 

 and Verdun, '99). Getzowa ('11), studying human thyreoids 

 which had become atrophic, believes that the ultimobranchial 

 body does not form thyreoid tissue, but remains cystic or entirely 

 degenerates. This view is also held by Kingsbury ('14). As to 

 the significance of the ultimobranchial body in man Kingsbury 

 says: 



Continued growth produces the blind pocket of pharyngeal ento- 

 derm termed the ultimobranchial body. • It may be described as pro- 

 duced by a continuation of the growth process in the pharyngeal ento- 

 derm, which as part of the differential growth of the region has formed 

 the successive branchial pockets. In its development it would from 

 this point of view be linked thus with the branchial region. It could 

 hardly represent in any morphological sense a rudimentary fifth pouch, 

 since it is or appears to be already present in the two embryos in which 

 a fifth pouch is shown. Nor does it seem to me that there is any bet- 

 ter reason for describing it as an appendage of a fifth pouch. Into it, 

 in later development would undoubtedly go the cells which actually 

 took part in a fifth ento-ectodermal contact, or might have done so 

 had it been developed. 



