660 FRANCIS M. BALDWIN 



obvious that upon the interpretation of the ultimobranchial body 

 as a branchiomeric organ, as a derivative of a rudimentary fifth 

 pouch, the 'ultimobranchial' structures of the lower vertebrates 

 cannot .represent it, since the fifth pouch may be a functional gill- 

 pouch in the amphibian." Rabl's ('11, '13) suggestion that i is 

 the representative of both fifth and sixth pouches in man, meets 

 with Kingsbury's objection, since, although it satisfies the hom- 

 ology between man .and amphibians, ' 'it fails as applied to the 

 elasmobranchs where the sixth pouch is a functional gill cleft 

 caudad of which occurs the suprapericardial body which appears 

 to be an ultimobranchial body (van Bemmelen ('89), Greil ('05))." 



' 'For those who view this structure as a vestigial ancestral gland 

 of some kind, Maurer's term and interpretation inherent therein 

 — postbranchial body — presents no such logical difficulty, since, 

 as Maurer ('11) said in defense of his term at the Leipzig meeting 

 of the Anatomische Gesellschaft, these structures might then be 

 homologized throughout the vertebrate series in the forms in 

 which they occur." The evidence, however, as Kingsbury sees 

 it, "indicates strongly that the structures .... belong 

 to the branchial region and are not 'postbranchial.' " The only 

 way then, "whereby these pharyngeal structures may be inter- 

 preted as ultimobranchial and also directly homologized in the 

 different vertebrates would seem to be the assumption, — that it is 

 the last branchial pouch which in the form of ultimobranchial 

 body or represented by it as a derivative has retained its individual 

 existence while the reduction in number of branchial pouches has 

 been brought about by the elimination of the gill clefts that pro- 

 ceeded it in the series. 



"The double assumption of this ]')haryngeal derivative as an 

 'ultimobranchial' body and as a vestigial gland representing an 

 ancestral organ .... can not be true on any morpho- 

 logical basis of homology." 



Kingsbury thus concludes that in man, ' 'no reason is seen for 

 considering the ultimobranchial body so called either as repre- 

 senting an ancestral gland, vestigial in mammals, or representing 

 any specific pouch, either V or VI, but merely formed by a con- 

 tinued growth activity in the branchial entoderm." 



