330 B. F. KINGSBUEY 



possesses rather negative characteristics. While the one cepha- 

 lad of it, the first or hyomandibular, develops into the middle 

 ear and eustachian tube (tuba auditiva) and those caudad of it 

 have the very interesting derivatives — ^thymus, parathyreoids, 

 so-called lateral thyreoid, etc. — the second pouch leaves no clear 

 and characteristic record in the bodily structure, save perhaps 

 the palatine tonsils, which appear to mark its site and to whose 

 appearance this branchial pocket may possibly bear some causal 

 relation. 



It is true that the second pharyngeal pouch gives rise to a 

 thymus body in anurous amphibia, among fishes, and according 

 to de Meuron, ('86) Van Bemmeln ('86), and K. Peter ('01), 

 in the Uzard; and that a parathyreoid or epithelial body is said 

 by Van Bemmeln to develop from it in snakes; while Maurer's 

 claim from the conditions found by him in Echidna and Anura 

 that the carotid body is, or represents, such an epithehal body 

 II (parathyreoid II), is hkewise a matter o*f record. Such find- 

 ings in lower forms but naturally suggest the presence of at 

 least potential thymus and parathyreoid elements in the second 

 pouch as well as in the third (and fourth) . Critical and careful 

 examination of the abundant material in the wslj of human and 

 higher manmial embryos in the past has failed to determine the 

 presence of traces of such structures belonging to the second 

 pouch (p. 3C0), and I may say at this point that careful ex- 

 amination by myself of the quite complete series of human 

 embryos used in this study but confirms the negative findings 

 of other workers. 



It would be but natural, however, in spite of negative evidence, 

 to consider that these structures, as branchiomeric organs, were 

 nevertheless potentially present. Particularly since the classical 

 study by Verdun ('98) these organs are frequently thought of 

 as branchiomeric organs, there being a thymus and a parathyreoid 

 (epithehal body) component belonging to each branchial pouch. 

 Such a conception would of necessity assume that these structures, 

 as such, were in some way intrinsic in the cells of the pharyngeal 

 entoderm metamerically arranged. Quite a different inter- 

 pretation, however, is possible. The second pouch, unlike the 



