440 



<^%i:±iiiO?^^==^^^==^^ 



5 »• ^ s 51;^ .^^ ■? 5" ~ i " * 



5-. y; -= « g s 



Fig. 6. Cross-section through the head of a frog (R. fusca) of 14 mm length, 

 parts dorsal to pharynx omitted, cp anläge of corpus propericardiale ; des M. deltoideus, 

 portio episternalis ; dkr dorsally situated branchial remnants ; es episternum ; h hyoid 

 cartilage; hn lymphoid masses representing the lymphoid knot uniformly present in the 

 ventral part of the branchial chamber of larval stages, biit persisting unusually late in 

 this specimen ; mkr branchial remains that a few sections posteriorly are connected with 



a ventrallv lying mass of 



bhb mg 



irpl 



ce si 



hg' 



sthy 



nidi 



rps 



II m hif 



branchial remnants; v. v. 

 large vein of the pseudo- 

 thyroid. Other parts as 

 in preceding figures. 



Fig. 7. Cross-sec- 

 tion througli the left 

 pseudothyroid body of a 

 frog (R. fusca) of 14 rnm 

 length , in which the 

 larval basihyo-branchialis 

 muscle has persisted until 

 remnants of it are sur- 

 rounded by the lymphoid 

 cells of the anläge of the 

 pseudothyroid body; bhb 

 fragments of fibres of basi- 

 hyo-branchialis muscle 

 surrounded by capillaries 

 and lymphoid cells ; mg 

 ramus musculo-glandula- 

 ris of the A. cai'otis ex- 

 terna. Other parts as in 

 preceding figures. 



mentioned. On each side is a continuation of the Vena pseudo- 

 thyreoidea; in the median line are vessels that later differentiate 

 into the Vena pericardiaca anterior, and a vein lying between 

 the hyoglossal muscles. At this stage the branches of the musculo- 

 glandular artery can not be distinguished from the veins. As devel- 

 opment progresses the blood vessels encroach more and more upon 

 the reticulum, tortuous lymph spaces make their appearance about 



