[THOMPSON] CERVICAL REGION OF THE FROG 63 
Meuron! for Rana and Bufo, and by Maurer? for Rana esculenta. 
Aceording to Miiller and Maurer the thyroid of the frog arises as an 
unpaired median evagination from the ventral pharyngeal epithelium 
in the neighbourhood of the second cleft. The unpaired organ finally 
divides into two. Further details and references are given by Gaupp. 

Schematic representation of the gill-clefts and their derivatives in the Anura. 
Car.b. carotid body. D.b.b. dorsal branchial body. 
M.b.b. median branchial body. Oes. oesophagus. 
P.b.b. —post branchial body. Pthyr. parathyroid. 
Thym.—thymus. Thyr. —thyroid. 
‘Accessory thyroids exist in the frog. I have not seen them with 
the naked eye; but have found them in serial sections cut through the 
thyroid region. Their microscopical structure is precisely that of the 
thyroid proper. 

1 Recueil Zoologique Suisse, T. 3, Genève, 1886. 
? Jenaische Denkschriften, Bd. 6, 1899. 
